.. _configuration:

###############
 Configuration
###############

tox configuration can be split into two categories: core and environment specific. Core settings are options that can be
set once and used for all tox environments, while environment options are applied to the given tox environment only.

.. _compatibility-requirements:

*********************
 System requirements
*********************

tox works with the following Python interpreter implementations:

- `CPython <https://www.python.org/>`_ versions 3.10, 3.11, 3.12, 3.13, 3.14

This means tox works on the latest patch version of each of these minor versions. Previous patch versions are supported
on a best effort approach.

**************************
 Discovery and file types
**************************

With regards to the configuration format, at the moment we support the following formats:

- `INI <https://en.wikipedia.org/wiki/INI_file>`_.
- `TOML <https://toml.io/en/v1.0.0>`_.

Out of box tox supports five configuration locations prioritized in the following order:

.. mermaid::

    flowchart TD
        search[tox searches current directory] --> tox_ini
        tox_ini[tox.ini — INI] -- not found --> setup_cfg[setup.cfg — INI]
        setup_cfg -- not found --> pyproject_native[pyproject.toml — tool.tox]
        pyproject_native -- not found --> pyproject_legacy[pyproject.toml — legacy_tox_ini]
        pyproject_legacy -- not found --> tox_toml[tox.toml — TOML]

        classDef ini fill:#dbeafe,stroke:#3b82f6,stroke-width:2px,color:#1e3a5f
        classDef toml fill:#dcfce7,stroke:#22c55e,stroke-width:2px,color:#14532d
        classDef start fill:#f3f4f6,stroke:#9ca3af,stroke-width:2px,color:#374151

        class tox_ini,setup_cfg,pyproject_legacy ini
        class pyproject_native,tox_toml toml
        class search start

1. ``tox.ini`` (INI),
2. ``setup.cfg`` (INI),
3. Native ``pyproject.toml`` under the ``tool.tox`` table (TOML),
4. ``pyproject.toml`` with the ``tool.tox`` table, having ``legacy_tox_ini`` key (containing INI),
5. ``tox.toml`` (TOML).

Historically, the INI format was created first, and TOML was added in 2024. **TOML is the recommended format for new
projects** -- it is more robust, has proper type support, and avoids ambiguities inherent in INI parsing (e.g.
multi-line values, comment escaping). INI remains supported and is more concise for some patterns.

.. _toml-feature-gaps:

Format comparison
=================

Both INI and TOML support the same features with different syntax. The only INI feature without a TOML equivalent is
generative section names (see below).

**Conditional factors** -- Both INI and TOML support filtering by factor name. A factor is any dash-separated segment in
the environment name (e.g. ``py313-django50`` has factors ``py313`` and ``django50``). Additionally, the current
platform (``sys.platform`` value like ``linux``, ``darwin``, ``win32``) is automatically available as an implicit
factor.

.. tab:: TOML

    .. code-block:: toml

        [env_run_base]
        deps = [
            "pytest",
            { replace = "if", condition = "factor.django50", then = ["Django>=5.0,<5.1"], extend = true },
            { replace = "if", condition = "factor.django42", then = ["Django>=4.2,<4.3"], extend = true },
            { replace = "if", condition = "not factor.lint", then = ["coverage"], extend = true },
        ]
        commands = [
            { replace = "if", condition = "factor.linux", then = [["python", "-c", "print('on linux')"]], extend = true },
            { replace = "if", condition = "factor.darwin", then = [["python", "-c", "print('on mac')"]], extend = true },
            { replace = "if", condition = "factor.win32", then = [["python", "-c", "print('on windows')"]], extend = true },
        ]

    Use ``replace = "if"`` with ``factor.NAME`` conditions. Supports boolean operations (``and``, ``or``, ``not``) and
    can combine with environment variable checks (``env.VAR``).

.. tab:: INI

    .. code-block:: ini

        [testenv]
        deps =
            pytest
            django50: Django>=5.0,<5.1
            django42: Django>=4.2,<4.3
            !lint: coverage
        commands =
            linux: python -c 'print("on linux")'
            darwin: python -c 'print("on mac")'
            win32: python -c 'print("on windows")'

    Supports simple factors (``django50:``), multiple factors (``py313,py312:``), and negation (``!lint:``). Any
    multi-line setting (``deps``, ``commands``, ``set_env``, etc.) can use factor conditions.

Platform factors work in any environment without requiring the platform name in the environment name.

**Generative environment lists** -- Both INI and TOML support generating environment lists from factor combinations.

.. tab:: TOML

    .. code-block:: toml

        env_list = [
            { product = [["py312", "py313", "py314"], ["django42", "django50"]] },
        ]

    The ``product`` dict computes the Cartesian product of its factor groups and joins each combination with ``-``.
    Range dicts (``{ prefix = "py3", start = 12, stop = 14 }``) and literal strings can be mixed in the same list.
    An optional ``exclude`` key skips specific combinations.

.. tab:: INI

    .. code-block:: ini

        [tox]
        env_list = py3{12,13,14}-django{42,50}

    Curly-brace expressions expand into the Cartesian product of all combinations. This generates 6 environments:
    ``py312-django42``, ``py312-django50``, ..., ``py314-django50``. Ranges are also supported: ``py3{12-14}`` expands
    to ``py312``, ``py313``, ``py314``. Open-ended ranges expand to the `supported CPython versions
    <https://devguide.python.org/versions/>`_ at the time of the tox release: ``py3{10-}`` expands up to the latest
    supported version, ``py3{-13}`` expands down to the oldest supported one.

**Generative section names** -- INI section headers can use the same curly-brace expansion:

.. code-block:: ini

    [testenv:py3{12,13}-{x86,x64}]
    envdir =
        x86: .venv-x86
        x64: .venv-x64

TOML does not support generative section names, but you can use ``env_base`` templates (see :ref:`env-base-templates`)
to generate multiple environments from a single definition:

.. code-block:: toml

    [env_base.build]
    factors = [["py312", "py313"], ["x86", "x64"]]
    env_dir = { replace = "if", condition = "factor.x86", then = ".venv-x86", "else" = ".venv-x64" }
    commands = [["python", "-c", "print('ok')"]]

This generates ``build-py312-x86``, ``build-py312-x64``, ``build-py313-x86``, ``build-py313-x64`` -- each inheriting
from the template and resolving factor conditions per environment.

.. _env-base-templates:

Environment base templates
--------------------------

``env_base`` sections define named templates that generate multiple environments from factor combinations. Each template
requires a ``factors`` key -- a list of factor groups whose Cartesian product determines which environments are created.
The template name is joined with each factor combination using ``-``:

.. code-block:: toml

    [env_base.test]
    factors = [["3.13", "3.14"]]
    deps = ["pytest>=8"]
    commands = [["pytest"]]

This generates ``test-3.13`` and ``test-3.14``. For multi-dimensional matrices:

.. code-block:: toml

    [env_base.django]
    factors = [["py312", "py313"], ["django42", "django50"]]
    deps = [
        "pytest",
        { replace = "if", condition = "factor.django42", then = ["Django>=4.2,<4.3"], extend = true },
        { replace = "if", condition = "factor.django50", then = ["Django>=5.0,<5.1"], extend = true },
    ]
    commands = [["pytest"]]

This generates 4 environments: ``django-py312-django42``, ``django-py312-django50``, ``django-py313-django42``,
``django-py313-django50``.

**Inheritance chain:** settings resolve in this order: ``[env.{name}]`` (explicit overrides) → ``[env_base.{template}]``
(template defaults) → ``[env_run_base]`` (global defaults).

**Factor groups** can be:

- A list of strings: ``["a", "b"]``
- A range dict: ``{ prefix = "py3", start = 12, stop = 14 }`` (generates ``py312``, ``py313``, ``py314``)
- A labeled dict: ``{ ecosystem = ["oci", "python"] }`` (same as a list, but registers the label for substitution)
- Mixed in the same ``factors`` list for Cartesian products

The template name itself does not appear as a runnable environment -- only the generated names do.

.. _factor-label-substitution:

Factor label substitution
^^^^^^^^^^^^^^^^^^^^^^^^^

.. versionadded:: 4.49.0

Factor groups can be labeled by using a single-key dict instead of a plain list. The label enables ``{factor:label}``
substitution in any string value (descriptions, commands, deps, set_env, etc.), resolving to whichever value from the
labeled group is an active factor in the current environment. Every factor group also receives a positional label
(``0``, ``1``, ...) automatically.

**Named labels** -- use a single-key dict to name a factor group:

.. code-block:: toml

    [env_base.sync]
    factors = [{ecosystem = ["oci", "python", "js"]}, {target = ["pw", "tt"]}]
    description = "Sync {factor:ecosystem} artifacts to {factor:target}"
    commands = [["sync-tool", "--ecosystem", "{factor:ecosystem}"]]

For ``sync-oci-pw``, the description resolves to ``Sync oci artifacts to pw`` and the command receives ``--ecosystem
oci``.

**Positional labels** -- plain lists automatically get index-based labels:

.. code-block:: toml

    [env_base.task]
    factors = [["oci", "python"], ["pw", "tt"]]
    description = "Run {factor:0} on {factor:1}"

For ``task-oci-pw``, the description resolves to ``Run oci on pw``. Labeled dicts also support positional access:
``{factor:0}`` and ``{factor:ecosystem}`` both resolve to ``oci`` when the labeled dict is in position 0.

**In product matrices** -- labeled factor groups work in ``env_list`` product dicts too:

.. code-block:: toml

    env_list = [
        { product = [["sync"], {ecosystem = ["oci", "python"]}, {target = ["pw", "tt"]}] },
    ]

    [env_run_base]
    description = "Sync {factor:ecosystem} to {factor:target}"

**Defaults** -- ``{factor:label:fallback}`` uses ``fallback`` when the label is unknown, following the same convention
as ``{env:VAR:default}``.

**Comparison with conditionals** -- ``{factor:label}`` replaces nested ``replace = "if"`` chains when the substituted
value equals the factor name itself. For values that don't match factor names (e.g., mapping ``pw`` to
``production-west-cluster``), use ``replace = "if"`` with ``factor.NAME`` conditions.

**Reserved names** -- the following cannot be used as label names: ``env``, ``posargs``, ``tty``, ``glob``, ``factor``.

.. _tox-ini:

``tox.ini``
===========

This configuration file uses:

- ``tox`` section to host core configuration,
- ``testenv:{env_name}`` section to host environment configuration,
- ``testenv`` section as base configuration for run environments (fallback location for missing values for a test/run
  environment),
- ``pkgenv`` section as base configuration for package environments (fallback location for missing values for a package
  environment).

For example:

.. code-block:: ini

    [tox]
    requires =
        tox >= 4.20
    env_list =
        3.14t
        3.14
        3.13
        3.12
        type

    [testenv]
    deps = pytest
    commands = pytest tests

    [testenv:type]
    deps = mypy
    commands = mypy src

``setup.cfg``
=============

This configuration file uses:

- ``tox:tox`` section to host core configuration,
- ``testenv:{env_name}`` section to host environment configuration,
- ``testenv`` section as base configuration for run environments (fallback location for missing values for a test/run
  environment),
- ``pkgenv`` section as base configuration for package environments (fallback location for missing values for a package
  environment).

.. code-block:: ini

    [tox:tox]
    requires =
        tox >= 4.0
    env_list =
        3.14t
        3.14
        3.13
        3.12
        type

    [testenv]
    deps = pytest
    commands = pytest tests

    [testenv:type]
    deps = mypy
    commands = mypy src

``pyproject.toml`` - INI
========================

This configuration file is equivalent to :ref:`tox.ini <tox-ini>` format, with the difference that the text is stored
instead inside the ``pyproject.toml`` file under the ``tool.tox`` table and ``legacy_tox_ini`` key:

.. code-block:: toml

    [tool.tox]
    legacy_tox_ini = """
        [tox]
        requires =
            tox >= 4.0
        env_list =
            3.14
            3.13
            3.12
            type

        [testenv]
        deps = pytest
        commands = pytest tests

        [testenv:type]
        deps = mypy
        commands = mypy src
    """

.. _pyproject-toml-native:

``pyproject.toml`` - native
===========================

We support native TOML configuration via the ``pyproject.toml`` files ``tool.tox`` table. This configuration file uses:

- ``tool.tox`` table to host core configuration,
- ``tool.tox.env.{env_name}`` table to host environment configuration,
- ``tool.tox.env_run_base`` table as base configuration for run environments (fallback location for missing values for a
  test/run environment),
- ``tool.tox.env_pkg_base`` table as base configuration for package environments (fallback location for missing values
  for a package environment).

.. code-block:: toml

    [tool.tox]
    requires = ["tox>=4.19"]
    env_list = ["3.14t", "3.14", "3.13", "3.12", "type"]

    [tool.tox.env_run_base]
    description = "Run test under {base_python}"
    commands = [["pytest"]]

    [tool.tox.env.type]
    description = "run type check on code base"
    deps = ["mypy==1.18.2", "types-cachetools>=5.5.0.20240820", "types-chardet>=5.0.4.6"]
    commands = [["mypy", "src{/}tox"], ["mypy", "tests"]]

``tox.toml``
============

This configuration file is equivalent to :ref:`pyproject.toml - native <pyproject-toml-native>` with the difference that
it lives in a separate dedicated files and accordingly the ``tool.tox`` sub-table is no longer required.

For example:

.. code-block:: toml

    requires = ["tox>=4.19"]
    env_list = ["3.14t", "3.14", "3.13", "3.12", "type"]

    [env_run_base]
    description = "Run test under {base_python}"
    commands = [["pytest"]]

    [env.type]
    description = "run type check on code base"
    deps = ["mypy==1.18.2", "types-cachetools>=5.5.0.20240820", "types-chardet>=5.0.4.6"]
    commands = [["mypy", "src{/}tox"], ["mypy", "tests"]]

.. _conf-core:

******
 Core
******

The following options are set in the ``[tox]`` section of ``tox.ini``, the ``[tox:tox]`` section of ``setup.cfg``, or
the top level of ``tox.toml``. Placing these options in an environment section (e.g. ``[testenv]``) has no effect. Run
``tox config`` or ``tox run -v`` to check for misplaced keys.

.. conf::
    :keys: requires
    :default: <empty list>
    :version_added: 3.2.0

    Specify a list of :pep:`508` compliant dependencies that must be satisfied in the Python environment hosting tox when
    running the tox command. If any of these dependencies are not satisfied will automatically create a provisioned tox
    environment that does not have this issue, and run the tox command within that environment. See
    :ref:`provision_tox_env` for more details.

     .. tab:: TOML

        .. code-block:: toml

           [tool.tox]
           requires = [
             "tox>=4",
             "virtualenv>20.2",
           ]

     .. tab:: INI

        .. code-block:: ini

         [tox]
         requires =
             tox>=4
             virtualenv>20.2

.. conf::
    :keys: min_version, minversion
    :default: <current version of tox>
    :version_deprecated: 4.28.0
    :version_added: 2.4

    **DEPRECATED** Prefer requiring a minimum tox version via :ref:`requires`.

    A string to define the minimal tox version required to run. If the host's tox version is less than this, it will
    automatically create a provisioned tox environment that satisfies this requirement. See :ref:`provision_tox_env`
    for more details.

.. conf::
    :keys: provision_tox_env
    :default: .tox
    :version_added: 3.8.0

    Name of the tox environment used to provision a valid tox run environment.

    .. note::

       The provisioning environment does not inherit settings from ``env_run_base`` (TOML) or ``[testenv]`` (INI).
       It must be explicitly configured if you need to customize it (e.g. ``env.".tox"`` in TOML or
       ``[testenv:.tox]`` in INI).

    .. versionchanged:: 3.23.0

       When tox is invoked with the ``--no-provision`` flag, the provision won't be attempted,  tox will fail instead.

.. conf::
    :keys: env_list, envlist
    :default: <empty list>
    :version_added: 1.0

    A list of environments to run by default (when the user does not specify anything during the invocation).

    .. versionchanged:: 3.4.0

       Which tox environments are run during the tox invocation can be further filtered via the operating system
       environment variable ``TOX_SKIP_ENV`` regular expression (e.g. ``py27.*`` means **don't** evaluate environments
       that start with the key ``py27``). Skipped environments will be logged at level two verbosity level.

.. conf::
    :keys: skip_missing_interpreters
    :default: config
    :version_added: 1.7.2

    Setting this to ``true`` will force ``tox`` to return success even if some of the specified environments were
    missing. This is useful for some CI systems or when running on a developer box, where you might only have a subset
    of all your supported interpreters installed but don't want to mark the build as failed because of it. As expected,
    the command line switch always overrides this setting if passed on the invocation. Setting it to ``config`` means
    that the value is read from the config file.

.. conf::
    :keys: tox_root, toxinidir
    :version_added: 1.6.1

    The root directory for the tox project (where the configuration file is found).

.. conf::
    :keys: work_dir, toxworkdir
    :default: {tox_root}/.tox
    :version_added: 1.0

    Directory for tox to generate its environments into, will be created if it does not exist.

.. conf::
    :keys: temp_dir
    :default: {work_dir}/.tmp
    :version_added: 3.5

    Directory where to put tox temporary files. For example: we create a hard link (if possible, otherwise new copy) in
    this directory for the project package. This ensures tox works correctly when having parallel runs (as each session
    will have its own copy of the project package - e.g. the source distribution).

.. conf::
    :keys: no_package, skipsdist
    :default: false
    :version_added: 1.6

    Flag indicating to perform the packaging operation or not. Set it to ``true`` when using tox for an application,
    instead of a library.

.. conf::
    :keys: package_env, isolated_build_env
    :default: .pkg
    :version_added: 3.3.0

     Default name of the virtual environment used to create a source distribution from the source tree.

.. conf::
    :keys: package_root, setupdir
    :default: {tox_root}
    :version_added: 1.0

     Indicates where the packaging root file exists (historically setup.py file or pyproject.toml now).

.. conf::
    :keys: labels
    :default: <empty dictionary>
    :version_added: 4.0

    A mapping of label names to environments it applies too. For example:

     .. tab:: TOML

        .. code-block:: toml

           [tool.tox]
           labels = { test = ["3.14t", "3.14", "3.13", "3.12"], static = ["ruff", "mypy"] }

     .. tab:: INI

        .. code-block:: ini

           [tox]
           labels =
                test = 3.14t, 3.14, 3.13, 3.12
                static = ruff, mypy

.. conf::
    :keys: on_platform
    :constant:
    :version_added: 4.17

    A constant holding the platform of the tox runtime environment.

Python language core options
============================

.. conf::
    :keys: ignore_base_python_conflict, ignore_basepython_conflict
    :default: False
    :version_added: 3.1

     .. versionadded:: 3.1.0

     tox allows setting the Python version for an environment via the :ref:`base_python` setting. If that's not set tox
     can set a default value from the environment name (e.g. ``3.10`` or ``py310`` implies Python 3.10). Matching up the Python
     version with the environment name has became expected at this point, leading to surprises when some configs don't
     do so. To help with sanity of users, an error will be raised whenever the environment name version does not match
     up with this expectation.

     Furthermore, we allow hard enforcing this rule by setting this flag to ``true``. In such cases we ignore the
     :ref:`base_python` and instead always use the base Python implied from the Python name. This allows you to configure
     :ref:`base_python` in the :ref:`base` section without affecting environments that have implied base Python versions.

     **This flag handles two types of conflicts:**

     1. **Explicit setting vs. environment name**: When :ref:`base_python` is explicitly set but conflicts with the
        version extracted from the environment name. Setting this to ``true`` uses the version from the environment name.

     2. **Multiple version factors in environment name** (since 4.47.3): When the environment name itself contains
        multiple factors that look like Python versions (e.g., ``unit-py3.10-2.16`` where both ``py3.10`` and ``2.16``
        match Python version patterns). Setting this to ``true`` falls back to :ref:`default_base_python` instead of
        raising an error. To avoid this ambiguity, prefix non-Python version factors (e.g. use ``ac2.16`` instead of
        ``2.16``).

.. _conf-testenv:

*****************
 tox environment
*****************

These are configuration for the tox environments (either packaging or run type). Set these in ``[testenv]`` (INI),
``env_run_base`` (TOML), or per-environment sections. Placing these options in the core ``[tox]`` section has no effect.
Run ``tox config`` or ``tox run -v`` to check for misplaced keys.

Base options
============

.. conf::
    :keys: envname, env_name
    :constant:
    :version_added: 4.0

    The name of the tox environment.

.. conf::
    :keys: env_dir, envdir
    :default: {work_dir}/{env_name}
    :version_added: 1.5

    Directory assigned to the tox environment. If not absolute it would be treated as relative to :ref:`tox_root`.

.. conf::
    :keys: env_tmp_dir, envtmpdir
    :default: {work_dir}/{env_name}/tmp
    :version_added: 0.5

    A folder that is always reset at the start of the run.

.. conf::
    :keys: env_log_dir, envlogdir
    :default: {work_dir}/{env_name}/log
    :version_added: 0.5

    A folder containing log files about tox runs. It's always reset at the start of the run. Currently contains every
    process invocation in the format of ``<index>-<run name>.log``, and details the execution request (command,
    environment variables, current working directory, etc.) and its outcome (exit code and standard output/error
    content).

.. conf::
    :keys: platform
    :version_added: 2.0

    Run on platforms that match this regular expression (empty means any platform). If a non-empty expression is defined
    and does not match against the ``sys.platform`` string the entire test environment will be skipped and none of the
    commands will be executed. Running ``tox -e <platform_name>`` will run commands for a particular platform and skip
    the rest.

.. conf::
    :keys: pass_env, passenv
    :default: <empty list>
    :version_added: 2.0

    Environment variables to pass on to the tox environment. The values are evaluated as UNIX shell-style wildcards, see
    `fnmatch <https://docs.python.org/3/library/fnmatch.html>`_  If a specified environment variable doesn't exist in the
    tox invocation environment it is ignored. The list of environment variable names is not case sensitive, for example:
    passing ``A`` or ``a`` will pass through both ``A`` and ``a``.

    Some variables are always passed through to ensure the basic functionality of standard library functions or tooling like
    pip. This is also not case sensitive on all platforms except Windows.

     .. list-table:: Environment Variables per Operating System
         :widths: 25 25 25 25
         :header-rows: 1

         *   - Environment Variable
             - Linux
             - MacOS
             - Windows
         *   - https_proxy
             - ✅
             - ✅
             - ✅
         *   - http_proxy
             - ✅
             - ✅
             - ✅
         *   - no_proxy
             - ✅
             - ✅
             - ✅
         *   - LANG
             - ✅
             - ✅
             - ✅
         *   - LANGUAGE
             - ✅
             - ✅
             - ✅
         *   - CURL_CA_BUNDLE
             - ✅
             - ✅
             - ✅
         *   - SSL_CERT_FILE
             - ✅
             - ✅
             - ✅
         *   - CC
             - ✅
             - ✅
             - ✅
         *   - CFLAGS
             - ✅
             - ✅
             - ✅
         *   - CCSHARED
             - ✅
             - ✅
             - ✅
         *   - CXX
             - ✅
             - ✅
             - ✅
         *   - CPPFLAGS
             - ✅
             - ✅
             - ✅
         *   - LD_LIBRARY_PATH
             - ✅
             - ✅
             - ✅
         *   - LDFLAGS
             - ✅
             - ✅
             - ✅
         *   - HOME
             - ✅
             - ✅
             - ✅
         *   - FORCE_COLOR
             - ✅
             - ✅
             - ✅
         *   - NO_COLOR
             - ✅
             - ✅
             - ✅
         *   - TMPDIR
             - ✅
             - ✅
             - ❌
         *   - TEMP
             - ❌
             - ❌
             - ✅
         *   - TMP
             - ❌
             - ❌
             - ✅
         *   - USERPROFILE
             - ❌
             - ❌
             - ✅
         *   - PATHEXT
             - ❌
             - ❌
             - ✅
         *   - MSYSTEM
             - ❌
             - ❌
             - ✅
         *   - WINDIR
             - ❌
             - ❌
             - ✅
         *   - APPDATA
             - ❌
             - ❌
             - ✅
         *   - LOCALAPPDATA
             - ❌
             - ❌
             - ✅
         *   - PROGRAMDATA
             - ❌
             - ❌
             - ✅
         *   - PROGRAMFILES(x86)
             - ❌
             - ❌
             - ✅
         *   - SYSTEMDRIVE
             - ❌
             - ❌
             - ✅
         *   - SYSTEMROOT
             - ❌
             - ❌
             - ✅
         *   - COMSPEC
             - ❌
             - ❌
             - ✅
         *   - PROCESSOR_ARCHITECTURE
             - ❌
             - ❌
             - ✅
         *   - NUMBER_OF_PROCESSORS
             - ❌
             - ❌
             - ✅
         *   - PIP_*
             - ✅
             - ✅
             - ✅
         *   - VIRTUALENV_*
             - ✅
             - ✅
             - ✅
         *   - NETRC
             - ✅
             - ✅
             - ✅
         *   - NIX_LD*
             - ✅
             - ✅
             - ❌
         *   - NIX_LD_LIBRARY_PATH
             - ✅
             - ✅
             - ❌
         *   - PYTHON_GIL
             - ✅
             - ✅
             - ✅
         *   - SSH_AGENT_PID
             - ✅
             - ✅
             - ❌
         *   - SSH_AUTH_SOCK
             - ✅
             - ✅
             - ❌

    If the environment variable ``CI`` is present, ``__TOX_ENVIRONMENT_VARIABLE_ORIGINAL_CI`` will be set to the value of ``CI``. The ``CI`` variable itself will not be passed through.

    More environment variable-related information can be found in :ref:`environment variable substitutions`.

.. conf::
    :keys: disallow_pass_env
    :default: <empty list>
    :version_added: 4.36

    Environment variable patterns to exclude after :ref:`pass_env` glob expansion. Uses the same
    :py:mod:`fnmatch` wildcard syntax as ``pass_env``. Applied after ``pass_env`` patterns are resolved against the
    host environment and before ``set_env`` values are applied:

    .. tab:: TOML

       .. code-block:: toml

          [env_run_base]
          pass_env = ["FOO_*"]
          disallow_pass_env = ["FOO_SECRET"]

    .. tab:: INI

       .. code-block:: ini

          [testenv]
          pass_env = FOO_*
          disallow_pass_env = FOO_SECRET

    In this example, all environment variables matching ``FOO_*`` are passed through except ``FOO_SECRET``.

.. conf::
    :keys: set_env, setenv
    :version_added: 1.0

    A dictionary of environment variables to set when running commands in the tox environment.

    In addition, there is an option to include an existing environment file. See the different syntax for TOML and INI below.

     .. tab:: TOML

        .. code-block:: toml

           [tool.tox.env_run_base]
           set_env = { file = "conf{/}local.env", TEST_TIMEOUT = "30" }

     .. tab:: INI

        .. code-block:: ini

           [testenv]
           set_env = file|conf{/}local.env
                TEST_TIMEOUT = 30


     The env file path may include previously defined tox variables:


     .. tab:: TOML

        .. code-block:: toml

           [tool.tox.env_run_base]
           set_env = { file = "{env:variable}" }

     .. tab:: INI

        .. code-block:: ini

           [testenv]
           set_env = file|{env:variable}


     .. note::

        Environment files are processed using the following rules:

        - blank lines are ignored,
        - lines starting with the ``#`` character are ignored,
        - each line is in KEY=VALUE format; both the key and the value are stripped,
        - there is no special handling of quotation marks, they are part of the key or value.

    **Conditional environment variables**

    .. versionadded:: 4.33

    Environment variables can be set conditionally based on PEP-508 environment markers. If the marker evaluates to
    false, the variable will not be set.

    .. note::

       Markers are evaluated against the Python interpreter running tox (the host Python), not the target environment's
       Python interpreter. This means markers like ``python_version`` reflect tox's Python version, not the target's.
       For platform-specific conditions (e.g., ``sys_platform``, ``os_name``), this is typically the desired behavior
       since the target environment runs on the same platform.

     .. tab:: TOML

        .. code-block:: toml

           [tool.tox.env_run_base]
           set_env.LINUX_VAR = { value = "1", marker = "sys_platform == 'linux'" }
           set_env.WIN_VAR = { value = "1", marker = "sys_platform == 'win32'" }

           # Can also be combined with replace directives
           set_env.CONDITIONAL = { replace = "env", name = "MY_VAR", default = "fallback", marker = "sys_platform == 'linux'" }

     .. tab:: INI

        .. code-block:: ini

           [testenv]
           set_env =
               LINUX_VAR = 1; sys_platform == 'linux'
               DARWIN_VAR = 1; sys_platform == 'darwin'
               WIN_ONLY = 1; sys_platform == 'win32'

    Available markers include ``sys_platform``, ``os_name``, ``platform_machine``, ``platform_system``,
    ``python_version``, ``implementation_name``, and others as defined in PEP-508.

    For conditional settings that should differ per target Python environment (e.g., based on Python version), use
    tox's :ref:`conditional settings <conditional-settings>` mechanism with environment factors instead.

    More environment variable-related information
    can be found in :ref:`environment variable substitutions`.

.. _injected-environment-variables:

Injected environment variables
------------------------------

tox automatically injects several environment variables into the test environment when running commands. These are
always set regardless of the ``pass_env`` or ``set_env`` configuration and cannot be overridden by the user.

.. list-table::
    :widths: 30 70
    :header-rows: 1

    - - Variable
      - Description
    - - ``TOX_ENV_NAME``
      - The name of the current tox environment (e.g. ``3.12``, ``lint``).
    - - ``TOX_WORK_DIR``
      - The tox working directory (by default ``.tox`` under the project root).
    - - ``TOX_ENV_DIR``
      - The directory of the current tox environment (e.g. ``.tox/3.12``).
    - - ``PYTHONIOENCODING``
      - Always set to ``utf-8`` to ensure consistent encoding for standard I/O.
    - - ``PIP_USER``
      - Always set to ``0`` to prevent pip from attempting ``--user`` installs inside virtualenvs, which would fail
        because user site-packages aren't visible. Only set when using ``virtualenv``\-based environments.
    - - ``TOX_PACKAGE``
      - The path(s) to the built package artifact(s), joined by ``os.pathsep`` if there are multiple. Only set in run
        environments where a package has been built. See :ref:`howto-reference-built-package` for usage examples.
    - - ``VIRTUAL_ENV``
      - The path to the virtual environment directory. Only set when using ``virtualenv``\-based environments (the
        default).
    - - ``__TOX_ENVIRONMENT_VARIABLE_ORIGINAL_CI``
      - The value of the ``CI`` environment variable from the host. Only set when the ``CI`` variable is present in the
        host environment.

.. note::

    In tox 3, ``TOX_PARALLEL_ENV`` was injected during parallel runs. This variable is **no longer injected** in tox 4.

.. conf::
    :keys: parallel_show_output
    :default: False
    :version_added: 3.7

    If set to ``True`` the content of the output will always be shown  when running in parallel mode.

.. conf::
    :keys: recreate
    :default: False
    :version_added: 0.9

    Always recreate virtual environment if this option is true, otherwise leave it up to tox.

.. conf::
    :keys: allowlist_externals
    :default: <empty list>
    :version_added: 1.5

    Each line specifies a command name (in glob-style pattern format) which can be used in the commands section even if
    it's located outside of the tox environment. For example: if you use the unix *rm* command for running tests you can
    list ``allowlist_externals=rm`` or ``allowlist_externals=/usr/bin/rm``. If you want to allow all external
    commands you can use ``allowlist_externals=*`` which will match all commands (not recommended).

.. conf::
    :keys: labels
    :default: <empty list>
    :ref_suffix: env
    :version_added: 4.0

    A list of labels to apply for this environment. For example:

     .. tab:: TOML

        .. code-block:: toml

           [tool.tox.env_run_base]
           labels = ["test", "core"]
           [tool.tox.env.flake8]
           labels = ["mypy"]

     .. tab:: INI

        .. code-block:: ini

           [testenv]
           labels = test, core
           [testenv:flake8]
           labels = mypy

Execute
=======

.. conf::
    :keys: suicide_timeout
    :default: 0.0
    :version_added: 3.15.2

     When an interrupt is sent via Ctrl+C or the tox process is killed with a SIGTERM, a SIGINT is sent to all foreground
     processes. The :ref:`suicide_timeout` gives the running process time to cleanup and exit before receiving (in some
     cases, a duplicate) SIGINT from tox.

.. conf::
    :keys: interrupt_timeout
    :default: 0.3
    :version_added: 3.15

     When tox is interrupted, it propagates the signal to the child process after :ref:`suicide_timeout` seconds. If the
     process still hasn't exited after :ref:`interrupt_timeout` seconds, its sends a SIGTERM.

.. conf::
    :keys: terminate_timeout
    :default: 0.2
    :version_added: 3.15

     When tox is interrupted, after waiting :ref:`interrupt_timeout` seconds, it propagates the signal to the child
     process, waits :ref:`interrupt_timeout` seconds, sends it a SIGTERM, waits :ref:`terminate_timeout` seconds, and
     sends it a SIGKILL if it hasn't exited.

Run
===

.. conf::
    :keys: base
    :default: testenv
    :version_added: 4.0.0

    Inherit missing keys from these sections.

.. conf::
    :keys: runner
    :default:
    :version_added: 4.0.0

    The tox execute used to evaluate this environment. Defaults to Python virtual environments, however may be
    overwritten by plugins.

.. conf::
    :keys: description
    :default: <empty string>
    :version_added: 2.7

    A short description of the environment, this will be used to explain the environment to the user upon listing
    environments.

.. conf::
    :keys: depends
    :default: <empty list>
    :version_added: 3.7

    tox environments that this environment depends on (must be run after those). Supports glob patterns using
    :py:mod:`fnmatch` syntax to match environment names dynamically:

    - ``*`` matches everything (e.g. ``3.*`` matches ``3.12``, ``3.13``, ``3.14``)
    - ``?`` matches any single character (e.g. ``py?`` matches ``py3`` but not ``py314``)
    - ``[seq]`` matches any character in *seq* (e.g. ``lint-[ab]`` matches ``lint-a`` and ``lint-b``)
    - ``[!seq]`` matches any character not in *seq*

    .. tab:: TOML

       .. code-block:: toml

          [env.coverage]
          depends = ["3.*"]

    .. tab:: INI

       .. code-block:: ini

          [testenv:coverage]
          depends = 3.*

    This matches all environments whose name starts with ``3.`` (e.g. ``3.12``, ``3.13``, ``3.14``). Glob patterns are
    resolved at runtime against the set of environments being run, so adding a new environment to ``env_list``
    automatically includes it in the dependency without updating ``depends``. Self-matches are excluded, so
    ``depends = *`` will depend on all other environments without creating a cycle.

    .. warning::

       ``depends`` does not pull in dependencies into the run target, for example if you select ``3.13,3.12,coverage``
       via the ``-e`` tox will only run those three (even if ``coverage`` may specify as ``depends`` other targets too -
       such as ``3.13, 3.12, 3.11``). This is solely meant to specify dependencies and order in between a target run
       set.

.. conf::
    :keys: extra_setup_commands
    :default: <empty list>
    :version_added: 4.37

    Commands to execute after the setup phase (dependencies and package installation) but before test commands.
    These commands run during the ``--notest`` phase, making them useful for separating environment setup from
    test execution. All evaluation and configuration logic applies from :ref:`commands`.

    This is particularly useful when you want to use ``tox run --notest`` to set up the environment and install
    additional tools or perform setup tasks, while keeping the actual test execution separate.

    For example, to install pre-commit hooks during the setup phase:

    .. tab:: TOML

       .. code-block:: toml

          [tool.tox.env_run_base]
          deps = ["pre-commit"]
          extra_setup_commands = [
            ["pre-commit", "install-hooks"],
          ]
          commands = [
            ["pre-commit", "run", "--all-files"],
          ]

    .. tab:: INI

       .. code-block:: ini

          [testenv]
          deps = pre-commit
          extra_setup_commands = pre-commit install-hooks
          commands = pre-commit run --all-files

    When running ``tox run --notest``, the environment will be created, dependencies installed, and
    ``extra_setup_commands`` executed, but ``commands`` will be skipped. When running ``tox run`` without
    ``--notest``, all commands including ``extra_setup_commands`` will execute.

.. conf::
    :keys: recreate_commands
    :default: <empty list>
    :version_added: 4.42

    Commands to run before the environment directory is removed during recreation (``tox run -r``). These commands
    execute inside the existing environment, so tools installed there are available. Useful for cleaning external caches
    managed by tools like pre-commit. Failures are logged as warnings but never block recreation.

    .. tab:: TOML

       .. code-block:: toml

          [env_run_base]
          deps = ["pre-commit"]
          recreate_commands = [["{env_python}", "-Im", "pre_commit", "clean"]]

    .. tab:: INI

       .. code-block:: ini

          [testenv]
          deps = pre-commit
          recreate_commands = {env_python} -Im pre_commit clean

    These commands do **not** run on first creation (the environment directory does not exist yet) or on normal
    re-runs without ``-r``.

.. conf::
    :keys: commands_pre
    :default: <empty list>
    :version_added: 3.4

    Commands to run before running the :ref:`commands`. All evaluation and configuration logic applies from
    :ref:`commands`.

.. conf::
    :keys: commands
    :default: <empty list>
    :version_added: 0.5

    The commands to be called for testing. Only execute if :ref:`commands_pre` succeed. Each line is interpreted as one
    command; however a command can be split over multiple lines by ending the line with the ``\`` character.

    Commands will execute one by one in sequential fashion until one of them fails (their exit code is non-zero) or all
    of them succeed. The exit code of a command may be ignored (meaning they are always considered successful) by
    prefixing the command with a dash (``-``) - this is similar to how ``make`` recipe lines work. The outcome of the
    environment is considered successful only if all commands (these + setup + teardown) succeeded (exit code ignored
    via the ``-`` or success exit code value of zero).

    .. note::

       The virtual environment binary path (see :ref:`env_bin_dir`) is prepended to the ``PATH`` environment variable,
       meaning commands will first try to resolve to an executable from within the virtual environment, and only after
       that outside of it. Therefore ``python`` translates as the virtual environments ``python`` (having the same
       runtime version as the :ref:`base_python`), and ``pip`` translates as the virtual environments ``pip``.

    .. note::

        ``shlex`` POSIX-mode quoting rules are used to split the command line into arguments on all
        supported platforms as of tox 4.4.0.

        The backslash ``\`` character can be used to escape quotes, whitespace, itself, and
        other characters (except on Windows, where a backslash in a path will not be interpreted as an escape).
        Unescaped single quote will disable the backslash escape until closed by another unescaped single quote.
        For more details, please see :doc:`shlex parsing rules <python:library/shlex>`.

    .. note::

      Inline scripts can be used, however note these are discovered from the project root directory, and is not
      influenced by :ref:`change_dir` (this only affects the runtime current working directory). To make this behavior
      explicit we recommend that you make inline scripts absolute paths by prepending ``{tox_root}``, instead of
      ``path/to/my_script`` prefer ``{tox_root}{/}path{/}to{/}my_script``. If your inline script is platform dependent
      refer to :ref:`platform-specification` on how to select different script per platform.

.. conf::
    :keys: commands_post
    :default: <empty list>
    :version_added: 3.4

    Commands to run after running the :ref:`commands`. Execute regardless of the outcome of both :ref:`commands` and
    :ref:`commands_pre`. All evaluation and configuration logic applies from :ref:`commands`.

.. conf::
    :keys: change_dir, changedir
    :default: {tox_root}
    :version_added: 0.5

    Change to this working directory when executing the test command. If the directory does not exist yet, it will be
    created (required for Windows to be able to execute any command).

.. conf::
    :keys: args_are_paths
    :default: False
    :version_added: 0.5

    Treat positional arguments passed to tox as file system paths and - if they exist on the filesystem and are in
    relative format - rewrite them according to the current and :ref:`change_dir` working directory. This handles
    automatically transforming relative paths specified on the CLI to relative paths respective of the commands executing
    directory.

.. conf::
    :keys: ignore_errors
    :default: False
    :version_added: 2.0

    When executing the commands keep going even if a sub-command exits with non-zero exit code. The overall status will
    be "commands failed", i.e. tox will exit non-zero in case any command failed. It may be helpful to note that this
    setting is analogous to the ``-k`` or ``--keep-going`` option of GNU Make.

.. conf::
    :keys: commands_retry
    :default: 0
    :version_added: 4.41

    Number of times to retry a failed command before giving up. A value of ``N`` means each command can be attempted up
    to ``N + 1`` times total. Applies to :ref:`commands_pre`, :ref:`commands`, and :ref:`commands_post`. Commands
    prefixed with ``-`` (ignore exit code) are never retried since their failures are already ignored.

    .. tab:: TOML

       .. code-block:: toml

          [env_run_base]
          commands_retry = 2
          commands = [["pytest", "tests"]]

    .. tab:: INI

       .. code-block:: ini

          [testenv]
          commands_retry = 2
          commands = pytest tests

.. conf::
    :keys: ignore_outcome
    :default: False
    :version_added: 2.2

    If set to true a failing result of this test environment will not make tox fail (instead just warn).

.. conf::
    :keys: fail_fast
    :default: False
    :version_added: 4.36.0

    If set to true, tox will stop executing remaining environments when this environment fails. This can also be
    enabled globally via the ``--fail-fast`` (``-x``) CLI flag. The behavior respects :ref:`ignore_outcome` --
    environments with ``ignore_outcome = true`` will not trigger fail-fast even if they fail.

.. conf::
    :keys: skip_install
    :default: False
    :version_added: 1.9

    Skip installation of the package. This can be used when you need the virtualenv management but do not want to
    install the current package into that environment. To also skip dependency installation at runtime, use the
    ``--skip-env-install`` CLI flag (see :ref:`skip-env-install`).

.. conf::
    :keys: package_env
    :default: {package_env}
    :version_added: 4.0.0
    :ref_suffix: env

    Name of the virtual environment used to create a source distribution from the source tree for this environment.

.. conf::
    :keys: package_tox_env_type
    :version_added: 4.0.0
    :default: virtualenv-pep-517

    tox package type used to package.

.. _packaging-env-config:

Packaging environment configuration
===================================

Packaging environments (such as ``.pkg`` and ``.pkg-cpython314``) are tox environments used to build your project's
package. Unlike run environments, packaging environments do **not** inherit from the ``env_run_base`` table (TOML) or
``[testenv]`` section (INI). This is intentional — test environment settings often conflict with packaging settings.

Instead, packaging environments inherit from the ``env_pkg_base`` table (TOML) or ``[pkgenv]`` section (INI). This
allows you to define common packaging settings in one central place, while still overriding them for specific packaging
environments when needed.

.. tab:: TOML

    .. code-block:: toml

       [env_pkg_base]
       pass_env = ["PKG_CONFIG", "PKG_CONFIG_PATH", "PKG_CONFIG_SYSROOT_DIR"]

       [env.".pkg-cpython311"]
       pass_env = ["PKG_CONFIG", "PKG_CONFIG_PATH", "PKG_CONFIG_SYSROOT_DIR", "IS_311"]

.. tab:: INI

    .. code-block:: ini

       [pkgenv]
       pass_env =
           PKG_CONFIG
           PKG_CONFIG_PATH
           PKG_CONFIG_SYSROOT_DIR

       [testenv:.pkg-cpython311]
       pass_env =
           {[pkgenv]pass_env}
           IS_311 = yes

.. note::

    Specific packaging environments are defined under ``[testenv:.pkg]`` and **not** ``[pkgenv:.pkg]``. The ``[pkgenv]``
    section (or ``env_pkg_base`` in TOML) serves only as the base/fallback for settings shared across all packaging
    environments.

.. versionchanged:: 4.2

    Packaging environments now inherit from the ``[pkgenv]`` / ``env_pkg_base`` section.

.. _python-options:

Python options
==============

.. conf::
    :keys: base_python, basepython
    :default: <{env_name} python factor> or <python version of tox>
    :version_added: 0.5

    Name or path to a Python interpreter which will be used for creating the virtual environment, first one found wins.
    This determines in practice the Python for what we'll create a virtual isolated environment. Use this to specify the
    Python version for a tox environment. If not specified, the virtual environments factors (e.g. name part) will be
    used to automatically set one. For example, ``py310`` means ``python3.10``, ``py3`` means ``python3`` and ``py``
    means ``python``. If the name does not match this pattern, :ref:`default_base_python` is consulted, and if that is
    also not set, the same Python version tox is installed into will be used.
    A base interpreter ending with ``t`` means that only free threaded Python implementations are accepted.

    The preferred naming convention is ``N.M`` (e.g. ``3.14``, ``3.13``) rather than ``pyNMM`` (e.g. ``py314``,
    ``py313``). The dotted form is clearer, avoids ambiguity for Python versions >= 3.10, and reads more naturally in
    environment lists and CI output.

    .. warning::

       Any factor matching the pattern ``2.N`` or ``3.N`` (where N is one or more digits) is treated as a Python
       version specifier. This means non-Python versions like ``2.16`` in an environment name such as
       ``unit-py3.10-2.16`` will conflict with the ``py3.10`` factor. To avoid this, prefix non-Python version numbers
       (e.g. ``ac2.16``), or set :ref:`ignore_base_python_conflict` to ``true``.

    .. versionadded:: 4.46

        You can append a CPU architecture (ISA) suffix to constrain the interpreter to a specific machine type. The
        architecture is derived from :func:`python:sysconfig.get_platform` and normalized by :pypi:`virtualenv` (e.g.
        ``amd64`` becomes ``x86_64``, ``aarch64`` becomes ``arm64``). Examples:

        - ``cpython3.12-64-arm64`` — CPython 3.12, 64-bit, ARM
        - ``cpython3.13-64-x86_64`` — CPython 3.13, 64-bit, x86-64

        If the discovered interpreter's architecture does not match the requested one, tox raises a failure, just as it
        does for version mismatches. This is useful on machines with multi-architecture support (e.g. Apple Silicon
        running both ``arm64`` and ``x86_64`` via Rosetta, or Linux with ``aarch64`` and ``x86_64`` via ``qemu-user``).

     .. versionchanged:: 3.1

         After resolving this value if the interpreter reports back a different version number than implied from the name
         a warning will be printed by default. However, if :ref:`ignore_basepython_conflict` is set, the value is
         ignored and we force the :ref:`base_python` implied from the factor name.

     .. note::

       Leaving this unset will cause an error if the package under test has a different Python requires than tox itself
       and tox is installed into a Python that's not supported by the package. For example, if your package requires
       Python 3.10 or later, and you install tox in Python 3.9, when you run a tox environment that has left this
       unspecified tox will use Python 3.9 to build and install your package which will fail given it requires 3.10.

.. conf::
    :keys: default_base_python
    :default: <python version of tox>
    :version_added: 4.42

    Fallback Python interpreter used when the environment name contains no Python factor and no explicit
    :ref:`base_python` is set. Accepts a list of specifications -- the first one found wins. This provides a way to
    pin a default Python version for reproducibility across different machines without conflicting with ``pyXY``
    factor-named environments.

    The resolution order for an environment's Python interpreter is:

    1. Python factor extracted from the environment name (e.g. ``3.13``, ``py313``)
    2. Explicit :ref:`base_python` setting on the environment
    3. :ref:`base_python_file` — read from a version file
    4. ``default_base_python`` (this setting)
    5. The Python running tox (``sys.executable``)

    .. tab:: TOML

        .. code-block:: toml

            [env_run_base]
            default_base_python = ["3.14", "3.13"]

    .. tab:: INI

        .. code-block:: ini

            [testenv]
            default_base_python = 3.14, 3.13

.. conf::
    :keys: base_python_file
    :default: <empty string>
    :version_added: 4.51

    A path to a file containing the Python version to use for the environment (e.g. ``.python-version``). The first
    non-blank, non-comment line in the file is used as the Python version specifier. This is useful for tool
    environments (such as ``mypy`` or ``coverage``) where you want a single source of truth for the default Python
    version without hardcoding it in the tox configuration.

    This option is only consulted when :ref:`base_python` is not explicitly set **and** the environment name does not
    contain a Python factor (e.g. ``py314``). See :ref:`default_base_python` for the full resolution order.

    .. tab:: TOML

       .. code-block:: toml

          [env.mypy]
          base_python_file = [".python-version", ".python-version-default"]

    .. tab:: INI

       .. code-block:: ini

          [testenv:mypy]
          base_python_file = .python-version, .python-version-default

    The file format is the same as used by ``pyenv`` and GitHub Actions' ``python-version-file``: one version per file,
    lines starting with ``#`` are comments, blank lines are ignored.

.. conf::
    :keys: env_site_packages_dir, envsitepackagesdir
    :constant:
    :version_added: 1.4.3

    The Python environments site package - where pure-python packages are installed (the purelib folder path).

.. conf::
    :keys: env_site_packages_dir_plat, envsitepackagesdir_plat
    :constant:
    :version_added: 4.42

    The Python environments platform-specific site package (the platlib folder path). On most platforms this is the same
    as :ref:`env_site_packages_dir`, but on some Linux distributions (Fedora, RHEL) platlib resolves to ``lib64`` instead
    of ``lib``.

.. conf::
    :keys: env_bin_dir, envbindir
    :constant:
    :version_added: 0.5

    The binary folder where console/gui scripts are generated during installation.

.. conf::
    :keys: env_python, envpython
    :constant:
    :version_added: 0.5

    The Python executable from within the tox environment.

.. conf::
    :keys: py_dot_ver
    :constant:
    :version_added: 4.0.10

    Major.Minor version of the Python interpreter in the tox environment (e.g., ``3.14``).

.. conf::
    :keys: py_impl
    :constant:
    :version_added: 4.0.10

    Name of the Python implementation in the tox environment in lowercase (e.g., ``cpython``, ``pypy``).

.. conf::
    :keys: py_free_threaded
    :constant:
    :version_added: 4.26

    ``True`` if the Python interpreter in the tox environment is a free-threaded CPython build,
    else ``False``.

Python run
==========

.. conf::
    :keys: dependency_groups
    :default: <empty list>
    :version_added: 4.22

    A list of names of dependency groups (as defined by :pep:`735`) to install into this Python environment. The
    installation will happen before installing the package or any of its dependencies.

    For example:

     .. tab:: TOML

        .. code-block:: toml

           [dependency-groups]
           test = [
              "pytest>=8",
           ]

           [tool.tox.env_run_base]
           dependency_groups = [
             "test",
           ]

     .. tab:: INI

        .. code-block:: ini

         [testenv]
         dependency_groups =
             test

        .. code-block:: toml

           [dependency-groups]
           test = [
              "pytest>=8",
           ]

.. conf::
    :keys: pylock
    :default: <empty string>
    :version_added: 4.44

    Path to a :pep:`751` ``pylock.toml`` lock file to install locked dependencies from. Mutually exclusive with
    :ref:`deps`. Each package in the lock file is filtered by evaluating its environment markers against the target
    Python interpreter and the configured :ref:`extras` and :ref:`dependency_groups`, then converted to a pinned
    requirement (``name==version``) and installed via pip with ``--no-deps``. The path is resolved relative to the
    :ref:`package_root` (or :ref:`tox_root` if no package root is configured). Change detection is automatic: adding,
    removing, or changing packages triggers environment recreation as needed. See :ref:`pylock-explanation` for details.

    For example:

     .. tab:: TOML

        .. code-block:: toml

           [tool.tox.env_run_base]
           pylock = "pylock.toml"

     .. tab:: INI

        .. code-block:: ini

         [testenv]
         pylock = pylock.toml

.. conf::
    :keys: deps
    :default: <empty list>
    :version_added: 0.5

    Python dependencies. Installed into the environment prior to project after environment creation, but
    before package installation. All installer commands are executed using the :ref:`tox_root` as the current working
    directory. Each value must be one of:

    - a Python dependency as specified by :pep:`440`,
    - a `requirement file <https://pip.pypa.io/en/stable/user_guide/#requirements-files>`_ when the value starts with
      ``-r`` (followed by a file path or URL),
    - a `constraint file <https://pip.pypa.io/en/stable/user_guide/#constraints-files>`_ when the value starts with
      ``-c`` (followed by a file path or URL).

    If you are only defining :pep:`508` requirements (aka no pip requirement files), you should use
    :ref:`dependency_groups` instead.

    For example:
     .. tab:: TOML

        .. code-block:: toml

           [tool.tox.env_run_base]
           deps = [
             "pytest>=8",
             "-r requirements.txt",
             "-c constraints.txt",
           ]

     .. tab:: INI

        .. code-block:: ini

         [testenv]
         deps =
             pytest>=7,<8
             -r requirements.txt
             -c constraints.txt

    .. note::

       :ref:`constraints` is the preferred way to specify constraints files since they will apply to package dependencies
       also.

.. conf::
    :keys: constraints
    :default: <empty list>
    :version_added: 4.28.0

    `Constraints files <https://pip.pypa.io/en/stable/user_guide/#constraints-files>`_ to use during package and
    dependency installation. Provided constraints files will be used when installing package dependencies and any
    additional dependencies specified in :ref:`deps`, but will not be used when installing the package itself.
    Each value must be a file path or URL.

.. conf::
    :keys: use_develop, usedevelop
    :default: false
    :version_added: 1.6

    Install the current package in development mode using :pep:`660`. This means that the package will
    be installed in-place and editable.

    .. note::

       ``package = editable`` is the preferred way to enable development/editable mode. See the details in :ref:`package`.

    .. note::

       PEP-660 introduced a standardized way of installing a package in development mode, providing the same effect as if
       ``pip install -e`` was used.

.. conf::
    :keys: package
    :version_added: 4.0

    When option can be one of ``wheel``, ``sdist``, ``sdist-wheel``, ``editable``, ``editable-legacy``, ``deps-only``,
    ``skip``, or ``external``. If :ref:`use_develop` is set this becomes a constant of ``editable``. If
    :ref:`skip_install` is set this becomes a constant of ``skip``.

    When ``deps-only`` is selected, tox installs the package's dependencies (including any requested :ref:`extras`) but
    does **not** build or install the package itself. This is useful for environments that need the same dependencies as
    the package without the package, such as coverage combining, documentation building, or linting. For projects with
    static :pep:`621` metadata in ``pyproject.toml``, dependencies are read directly without creating a packaging
    environment. For dynamic dependencies or non-PEP-621 projects, the packaging environment is used to extract
    metadata.

    When ``sdist-wheel`` is selected, tox first builds a source distribution and then builds a wheel from that sdist
    (rather than directly from the source tree). This is useful for verifying that the sdist is complete and that the
    package can be correctly built from it — catching missing files or packaging errors early.

    When ``editable`` is selected and the build backend supports :pep:`660`, tox will use the standardized editable
    install mechanism. If the backend does not support :pep:`660`, tox will automatically fall back to
    ``editable-legacy`` mode (equivalent to ``pip install -e``) and print a message suggesting you make this setting
    explicit in your configuration. To ensure your backend supports the standardized method, verify it meets the minimum
    version requirement (e.g. ``setuptools>=64``).

.. conf::
    :keys: wheel_build_env
    :version_added: 4.0
    :default: <package_env>-<python-flavor-lowercase><python-version-no-dot>

    If :ref:`package` is set to ``wheel`` or ``sdist-wheel`` this will be the tox Python environment in which the wheel
    will be built. For ``sdist-wheel``, the sdist is first built in the :ref:`package_env` environment, then the wheel
    is built from the extracted sdist in this environment. The value is generated to be unique per Python flavor and
    version, and prefixed with :ref:`package_env` value.
    This is to ensure the target interpreter and the generated wheel will be compatible. If you have a wheel that can be
    reused across multiple Python versions set this value to the same across them (to avoid building a new wheel for
    each one of them).

.. conf::
    :keys: extras
    :version_added: 2.4
    :default: <empty list>

    A list of "extras" from the package to be installed. For example, ``extras = testing`` is equivalent to ``[testing]``
    in a ``pip install`` command.

.. _external-package-builder:

External package builder
========================

tox supports operating with externally built packages. External packages might be provided in two ways:

- explicitly via the :ref:`--installpkg <tox-run---installpkg>` CLI argument,
- setting the :ref:`package` to ``external`` and using a tox packaging environment named ``<package_env>_external`` (see
  :ref:`package_env`) to build the package. The tox packaging environment takes all configuration flags of a
  :ref:`python environment <python-options>`, plus the following:

.. conf::
    :keys: deps
    :default: <empty list>
    :ref_suffix: external
    :version_added: 0.5

    Name of the Python dependencies as specified by :pep:`440`. Installed into the environment prior running the build
    commands. All installer commands are executed using the :ref:`tox_root` as the current working directory.

.. conf::
    :keys: commands
    :default: <empty list>
    :ref_suffix: external
    :version_added: 0.5

    Commands to run that will build the package. If any command fails the packaging operation is considered failed and
    will fail all environments using that package.

.. conf::
    :keys: ignore_errors
    :default: False
    :ref_suffix: external
    :version_added: 2.0

    When executing the commands keep going even if a sub-command exits with non-zero exit code. The overall status will
    be "commands failed", i.e. tox will exit non-zero in case any command failed. It may be helpful to note that this
    setting is analogous to the ``-k`` or ``--keep-going`` option of GNU Make.

.. conf::
    :keys: change_dir, changedir
    :default: {tox_root}
    :ref_suffix: external
    :version_added: 0.5

    Change to this working directory when executing the package build command. If the directory does not exist yet, it
    will be created (required for Windows to be able to execute any command).

.. conf::
    :keys: package_glob
    :default: {envtmpdir}{/}dist{/}*
    :version_added: 4.0

    A glob that should match the wheel/sdist file to install. If no file or multiple files is matched the packaging
    operation is considered failed and will raise an error.

Python virtual environment
==========================

.. conf::
    :keys: system_site_packages, sitepackages
    :default: False
    :version_added: 0.8

    Create virtual environments that also have access to globally installed packages. Note the default value may be
    overwritten by the ``VIRTUALENV_SYSTEM_SITE_PACKAGES`` environment variable.

    .. warning::

      In cases where a command line tool is also installed globally you have to make sure that you use the tool installed
      in the virtualenv by using ``python -m <command line tool>`` (if supported by the tool) or
      ``{env_bin_dir}/<command line tool>``. If you forget to do that you will get an error.

.. conf::
    :keys: always_copy, alwayscopy
    :default: False
    :version_added: 2.6

    Force virtualenv to always copy rather than symlink. Note the default value may be overwritten by the
    ``VIRTUALENV_COPIES`` or ``VIRTUALENV_ALWAYS_COPY`` (in that order) environment variables.  This is useful for
    situations where hardlinks don't work (e.g. running in VMS with Windows guests).

.. conf::
    :keys: download
    :version_added: 3.10
    :default: False

    True if you want virtualenv to upgrade pip/wheel/setuptools to the latest version. Note the default value may be
    overwritten by the ``VIRTUALENV_DOWNLOAD`` environment variable. If (and only if) you want to choose a specific
    version (not necessarily the latest) then you can add ``VIRTUALENV_PIP=20.3.3`` (and similar) to your :ref:`set_env`.

.. conf::
    :keys: virtualenv_spec
    :default: ""
    :version_added: 4.42

    A :pep:`440` version specifier for virtualenv (e.g. ``virtualenv<20.22.0``). When set, tox bootstraps the specified
    virtualenv version into an isolated environment and drives it via subprocess, instead of using the imported
    virtualenv library. This enables environments targeting Python versions that are incompatible with the virtualenv
    installed alongside tox.

    The bootstrap environment is cached under ``.tox/.virtualenv-bootstrap/`` (keyed by a hash of the spec string) and
    reused across runs. Concurrent access is protected by a file lock. When the spec is empty (the default), tox uses
    the imported virtualenv with zero overhead.

    .. tab:: TOML

        .. code-block:: toml

            [env.legacy]
            base_python = ["python3.6"]
            virtualenv_spec = "virtualenv<20.22.0"
            commands = [["python", "-c", "import sys; print(sys.version)"]]

            [env.modern]
            base_python = ["python3.15"]
            commands = [["python", "-c", "import sys; print(sys.version)"]]

    .. tab:: INI

        .. code-block:: ini

            [testenv:legacy]
            base_python = python3.6
            virtualenv_spec = virtualenv<20.22.0
            commands = python -c 'import sys; print(sys.version)'

            [testenv:modern]
            base_python = python3.15
            commands = python -c 'import sys; print(sys.version)'

    Changing this value triggers automatic environment recreation (the spec is included in the cache key).

    See :ref:`virtualenv-version-pinning` for background on when and why to use this setting.

Python virtual environment packaging
====================================

.. conf::
    :keys: meta_dir
    :version_added: 4.0.0
    :default: {env_dir}/.meta

    Directory where to put the project metadata files.

.. conf::
    :keys: pkg_dir
    :version_added: 4.0.0
    :default: {env_dir}/.dist

    Directory where to put project packages.

.. conf::
    :keys: config_settings_get_requires_for_build_sdist
    :version_added: 4.11

    Config settings (``dict[str, str]``) passed to the ``get_requires_for_build_sdist`` backend API endpoint.

.. conf::
    :keys: config_settings_build_sdist
    :version_added: 4.11

    Config settings (``dict[str, str]``) passed to the ``build_sdist`` backend API endpoint.

.. conf::
    :keys: config_settings_get_requires_for_build_wheel
    :version_added: 4.11

    Config settings (``dict[str, str]``) passed to the ``get_requires_for_build_wheel`` backend API endpoint.

.. conf::
    :keys: config_settings_prepare_metadata_for_build_wheel
    :version_added: 4.11

    Config settings (``dict[str, str]``) passed to the ``prepare_metadata_for_build_wheel`` backend API endpoint.

.. conf::
    :keys: config_settings_build_wheel
    :version_added: 4.11

    Config settings (``dict[str, str]``) passed to the ``build_wheel`` backend API endpoint.

.. conf::
    :keys: config_settings_get_requires_for_build_editable
    :version_added: 4.11

    Config settings (``dict[str, str]``) passed to the ``get_requires_for_build_editable`` backend API endpoint.

.. conf::
    :keys: config_settings_prepare_metadata_for_build_editable
    :version_added: 4.11

    Config settings (``dict[str, str]``) passed to the ``prepare_metadata_for_build_editable`` backend API endpoint.

.. conf::
    :keys: config_settings_build_editable
    :version_added: 4.11

    Config settings (``dict[str, str]``) passed to the ``build_editable`` backend API endpoint.

.. conf::
    :keys: fresh_subprocess
    :version_added: 4.14.0
    :default: True if build backend is setuptools otherwise False

    A flag controlling if each call to the build backend should be done in a fresh subprocess or not (especially older
    build backends such as ``setuptools`` might require this to discover newly provisioned dependencies).

Pip installer
=============

.. conf::
    :keys: install_command
    :default: python -I -m pip install {opts} {packages}
    :version_added: 1.6

    Determines the command used for installing packages into the virtual environment; both the package under test and its
    dependencies (defined with :ref:`deps`). Must contain the substitution key ``{packages}`` which will be replaced by
    the package(s) to install.  You should also accept ``{opts}`` -- it will contain index server options such as
    ``--pre`` (configured as ``pip_pre``).

    .. note::

       You can also provide arbitrary commands to the ``install_command``. Please take care that these commands can be
       executed on the supported operating systems. When executing shell scripts we recommend to not specify the script
       directly but instead pass it to the appropriate shell as argument (e.g. prefer ``bash script.sh`` over
       ``script.sh``).

.. conf::
    :keys: list_dependencies_command
    :default: python -m pip freeze --all
    :version_added: 2.4

    The ``list_dependencies_command`` setting is used for listing the packages installed into the virtual environment.
    This command will be executed only if executing on Continuous Integrations is detected (for example set environment
    variable ``CI=1``) or if journal is active. In TOML configurations, reference this Command value using
    ``{replace = "ref"}`` with ``extend = true`` rather than string interpolation.

.. conf::
    :keys: pip_pre
    :default: false
    :version_added: 1.9

    If ``true``, adds ``--pre`` to the ``opts`` passed to :ref:`install_command`. This will cause it to install the
    latest available pre-release of any dependencies without a specified version. If ``false``, pip will only install
    final releases of unpinned dependencies.

.. conf::
    :keys: constrain_package_deps
    :default: false
    :version_added: 4.4.0

    If ``constrain_package_deps`` is true, then tox will create and use ``{env_dir}{/}constraints.txt`` when installing
    package dependencies during ``install_package_deps`` stage. When this value is set to false, any conflicting package
    dependencies will override explicit dependencies and constraints passed to :ref:`deps`.

.. conf::
    :keys: use_frozen_constraints
    :default: false
    :version_added: 4.4.0

    When ``use_frozen_constraints`` is true, then tox will use the ``list_dependencies_command`` to enumerate package
    versions in order to create ``{env_dir}{/}constraints.txt``. Otherwise the package specifications explicitly listed
    under ``deps`` (or in requirements / constraints files referenced in ``deps``) will be used as the constraints. If
    ``constrain_package_deps`` is false, then this setting has no effect.

********************
 User configuration
********************

tox allows creation of user level config-file to modify default values of the CLI commands. It is located in the
OS-specific user config directory under ``tox/config.ini`` path, see ``tox --help`` output for exact location. It can be
changed via ``TOX_USER_CONFIG_FILE`` environment variable. Example configuration:

.. code-block:: ini

    [tox]
    skip_missing_interpreters = true

*****************************************
 Set CLI flags via environment variables
*****************************************

All configuration can be overridden via environment variables too, the naming convention here is ``TOX_<option>``. E.g.
``TOX_WORK_DIR`` sets the ``--workdir`` flag, or ``TOX_OVERRIDE`` sets the ``--override`` flag. For flags accepting more
than one argument, use the ``;`` character to separate these values:

All configuration inside the configuration file may be overwritten via the ``TOX_OVERRIDE``, note in this case the
configuration file and its access (section/table + key) are needed. Here we demonstrate with a ``tox.ini`` file:

.. code-block:: bash

    # set FOO and bar as passed environment variable
    $ env 'TOX_OVERRIDE=testenv.pass_env=FOO,BAR' tox c -k pass_env -e py
    [testenv:py]
    pass_env =
      BAR
      FOO
      <default pass_envs>

.. code-block:: bash

    # append FOO and bar as passed environment variable to the list already defined in
    # the tox configuration
    $ env 'TOX_OVERRIDE=testenv.pass_env+=FOO,BAR' tox c -k pass_env -e py
    [testenv:py]
    pass_env =
      BAR
      FOO
      <pass_envs defined in configuration>
      <default pass_envs>

.. code-block:: bash

    # set httpx and deps to and 3.12 as base_python
    $ env 'TOX_OVERRIDE=testenv.deps=httpx;testenv.base_python=3.12' .tox/dev/bin/tox c \
          -k deps base_python -e py
    [testenv:py]
    deps = httpx
    base_python = 3.12

************************************************
 Overriding configuration from the command line
************************************************

You can override options in the configuration file, from the command line. For example, given this config:

.. tab:: TOML

    .. code-block:: toml

        # tox.toml
       [env_run_base]
       deps = ["pytest"]
       set_env = { foo = "bar" }
       commands = [[ "pytest", "tests" ]]

.. tab:: INI

    .. code-block:: ini

     [testenv]
     deps = pytest
     set_env =
       foo=bar
     commands = pytest tests

You could enable ``ignore_errors`` by running:

.. tab:: TOML

    .. code-block:: bash

       tox --override env_run_base.ignore_errors=True

.. tab:: INI

    .. code-block:: bash

       tox --override testenv.ignore_errors=True

You could add additional dependencies by running:

.. tab:: TOML

    .. code-block:: bash

       tox --override env_run_base.deps+=pytest-xdist

.. tab:: INI

    .. code-block:: bash

       tox --override testenv.deps+=pytest-xdist

You could set additional environment variables by running:

.. tab:: TOML

    .. code-block:: bash

       tox --override env_run_base.set_env+=baz=quux

.. tab:: INI

    .. code-block:: bash

       tox --override testenv.set_env+=baz=quux

You can specify overrides multiple times on the command line to append multiple items:

.. tab:: TOML

    .. code-block:: bash

       tox -x env_run_base.set_env+=foo=bar -x env_run_base.set_env+=baz=quux
       tox -x testenv_run_baseenv.deps+=pytest-xdist -x env_run_base.deps+=pytest-covt

.. tab:: INI

    .. code-block:: bash

       tox -x testenv.set_env+=foo=bar -x testenv.set_env+=baz=quux
       tox -x testenv.deps+=pytest-xdist -x testenv.deps+=pytest-covt

Or reset override and append to that (note the first override is ``=`` and not ``+=``):

.. tab:: TOML

    .. code-block:: bash

       tox -x env_run_base.deps=pytest-xdist -x env_run_base.deps+=pytest-cov

.. tab:: INI

    .. code-block:: bash

       tox -x testenv.deps=pytest-xdist -x testenv.deps+=pytest-cov

***********
 TOML only
***********

These additional rules are active for native TOML configuration files.

String elements (excluding keys) will be transformed according to the :ref:`Substitutions <substitution>` section.

String substitution references
==============================

.. versionadded:: 4.21

Within strings values from other sections can be referred to via ``{[<table>]<key>}``:

which you can use to avoid repetition of config values. You can put default values in one section and reference them in
others to avoid repeating the same values:

.. code-block:: toml

    [extra]
    ok = "o"
    [.env.B]
    description = "{[extra]ok}"

If the target table is one of the tox environments variable substitution will be applied on the replaced value,
otherwise the text will be inserted as is (e.g., here with extra).

Configuration reference
=======================

.. versionadded:: 4.21

You can reference other configurations via the ``ref`` replacement. This can either be of type:

- ``env``, in this case the configuration is loaded from another tox environment, where string substitution will happen
  in that environments scope:

      .. code-block:: toml

          [env.src]
          extras = ["A", "{env_name}"]
          [env.dest]
          extras = [{ replace = "ref", env = "src", key = "extras", extend = true }, "B"]

  In this case ``dest`` environments ``extras`` will be ``A``, ``src``, ``B``.

- ``raw``, in this case the configuration is loaded as raw, and substitution executed in the current environments scope:

      .. code-block:: toml

          [env.src]
          extras = ["A", "{env_name}"]
          [env.dest]
          extras = [{ replace = "ref", of = ["env", "src", "extras"], extend = true }, "B"]

  In this case ``dest`` environments ``extras`` will be ``A``, ``dest``, ``B``.

The ``extend`` flag controls if after replacement the value should be replaced as is in the host structure (when flag is
false -- by default) or be extended into. This flag only operates when the host is a list.

When referencing Command-type configuration values (like ``list_dependencies_command``), the reference automatically
extracts the command's argument list, making it compatible with TOML's structured ``commands`` format. For example:

    .. code-block:: toml

        [tool.tox.env.a]
        package = "skip"
        commands = [[{ replace = "ref", env = "a", key = "list_dependencies_command", extend = true }]]

This expands the Command's args into the command list, avoiding the need for string interpolation which doesn't work
properly with Command values in TOML.

Positional argument reference
=============================

.. versionadded:: 4.21

You can reference positional arguments via the ``posargs`` replacement:

.. code-block:: toml

    [env.A]
    commands = [["python", { replace = "posargs", default = ["a", "b"], extend = true } ]]

If the positional arguments are not set commands will become ``python a b``, otherwise will be ``python posarg-set``.
The ``extend`` option instructs tox to unroll the positional arguments within the host structure. Without it the result
would become ``["python", ["a", "b"]`` which would be invalid.

Note that:

.. code-block:: toml

    [env.A]
    commands = [["python", "{posargs}" ]]

Differs in sense that the positional arguments will be set as a single argument, while in the original example they are
passed through as separate.

Empty commands groups will be ignored:

.. code-block:: toml

    [env.A]
    commands = [[], ["pytest"]]

will only invoke pytest. This is especially useful together with posargs allowing you to opt out of running a set of
commands:

    .. code-block:: toml

        [env.A]
        commands = [
            { replace = "posargs", default = ["python", "patch.py"]},
            ["pytest"]
        ]

When running ``tox run -e A`` it will invoke ``python patch.py`` followed by pytest. When running ``tox run -e A --`` it
will invoke only pytest.

Environment variable reference
==============================

.. versionadded:: 4.21

You can reference environment variables via the ``env`` replacement:

.. code-block:: toml

    [env.A]
    set_env.COVERAGE_FILE = { replace = "env", name = "COVERAGE_FILE", default = "ok" }

If the environment variable is set the the ``COVERAGE_FILE`` will become that, otherwise will default to ``ok``.

References within set_env
=========================

.. versionadded:: 4.21.1

When you want to inherit ``set_env`` from another environment you can use the feature that if you pass a list of
dictionaries to ``set_env`` they will be merged together, for example:

.. code-block:: toml

    [tool.tox.env_run_base]
    set_env = { A = "1", B = "2"}

    [tool.tox.env.magic]
    set_env = [
        { replace = "ref", of = ["tool", "tox", "env_run_base", "set_env"]},
        { C = "3", D = "4"},
    ]

Here the ``magic`` tox environment will have both ``A``, ``B``, ``C`` and ``D`` environments set.

Glob pattern reference
======================

.. versionadded:: 4.40

You can expand file system glob patterns via the ``glob`` replacement. Matched paths are sorted for deterministic
output, and relative patterns are resolved against ``tox_root``. The ``**`` wildcard matches any number of directories
recursively.

.. code-block:: toml

    [env.A]
    commands = [["twine", "upload", { replace = "glob", pattern = "dist/*.whl", extend = true }]]

When used with ``extend = true`` the matched files are expanded as separate arguments in the host list. Without
``extend`` the matches are joined as a single space-separated string.

If no files match and a ``default`` is provided it will be used as fallback:

.. code-block:: toml

    [env.A]
    commands = [["twine", "upload", { replace = "glob", pattern = "dist/*.whl", default = ["fallback.whl"], extend = true }]]

When no files match and no default is given, the result is an empty string (or empty list with ``extend``).

.. _conditional-value-reference:

Conditional value reference
===========================

.. versionadded:: 4.40 Conditional value replacement with ``env.VAR`` lookups.

.. versionchanged:: 4.42 Added ``factor.NAME`` lookups for environment name factors and platform.

.. versionchanged:: 4.50 Added ``factor['NAME']`` and ``env['VAR']`` subscript syntax and ``env_name`` variable.

You can conditionally select values based on environment variables and factors via the ``if`` replacement. The
``condition`` field accepts an expression language that supports ``env.VAR_NAME`` lookups for environment variables,
``factor.NAME`` lookups for environment name factors and platform, ``==``/``!=`` comparisons, and ``and``/``or``/``not``
boolean logic.

**Check if an environment variable is set (non-empty):**

.. code-block:: toml

    [env.A]
    set_env.MATURITY = { replace = "if", condition = "env.TAG_NAME", then = "production", "else" = "testing" }

If ``TAG_NAME`` is set and non-empty, ``MATURITY`` becomes ``production``, otherwise ``testing``.

**Compare an environment variable to a value:**

.. code-block:: toml

    [env.A]
    set_env.MODE = { replace = "if", condition = "env.CI == 'true'", then = "ci", "else" = "local" }

**Combine conditions with boolean logic:**

.. code-block:: toml

    [env.A]
    set_env.DEPLOY_TARGET = { replace = "if", condition = "env.CI and env.DEPLOY", then = "production", "else" = "none" }

    [env.B]
    pass_env = [{ replace = "if", condition = "env.CI or env.LOCAL", then = ["AWS_*"], "else" = [], extend = true }]

    [env.C]
    commands = [["pytest", { replace = "if", condition = "not env.CI", then = ["--pdb"], "else" = [], extend = true }]]

    [env.D]
    set_env.LOG_LEVEL = { replace = "if", condition = "env.MODE != 'prod'", then = "DEBUG", "else" = "INFO" }

**Omitting the else clause** defaults to an empty string:

.. code-block:: toml

    [env.A]
    set_env.DEPLOY_FLAG = { replace = "if", condition = "env.DEPLOY", then = "1" }

**Nested substitutions** in ``then``/``else`` values are processed normally:

.. code-block:: toml

    [env.A]
    set_env.TEST_ENV = { replace = "if", condition = "env.DEPLOY", then = "{env_name}", "else" = "local" }

**With extend in list contexts:**

.. code-block:: toml

    [env.A]
    commands = [["pytest", { replace = "if", condition = "env.VERBOSE", then = ["--verbose", "--debug"], "else" = ["--quiet"], extend = true }]]

**Check if a factor is present:**

.. code-block:: toml

    [env_run_base]
    deps = [
        "pytest",
        { replace = "if", condition = "factor.django50", then = ["Django>=5.0,<5.1"], extend = true },
    ]

If the environment name contains ``django50`` (e.g., ``py313-django50``), the Django dependency is added.

**Check for platform factors:**

.. code-block:: toml

    [env_run_base]
    commands = [
        { replace = "if", condition = "factor.linux", then = [["pytest", "--numprocesses=auto"]], extend = true },
        { replace = "if", condition = "not factor.linux", then = [["pytest"]], extend = true },
    ]

The current platform (``sys.platform`` value like ``linux``, ``darwin``, ``win32``) is automatically available as a
factor without requiring it in the environment name.

**Combine factor conditions with environment variables:**

.. code-block:: toml

    [env_run_base]
    commands = [["pytest", { replace = "if", condition = "factor.linux and env.CI", then = ["--numprocesses=auto"], "else" = [], extend = true }]]

**Check factors with non-identifier names:**

Factor names like ``3.14`` are not valid Python identifiers, so ``factor.3.14`` would be a syntax error. Use subscript
syntax instead:

.. code-block:: toml

    [env."test-3.14"]
    commands = [
        ["pytest", { replace = "if", condition = "factor['3.14']", then = ["--strict-markers"], "else" = [], extend = true }],
    ]

In this example, the environment name ``test-3.14`` has factors ``test`` and ``3.14``. The subscript syntax also works
for environment variables: ``env['CI']`` is equivalent to ``env.CI``.

**Check the environment name:**

Use ``env_name`` to match the full environment name as a string:

.. code-block:: toml

    [env_run_base]
    set_env.CUSTOM_FLAG = { replace = "if", condition = "env_name == 'test-3.14'", then = "enabled", "else" = "" }

**Condition expression reference:**

- ``env.VAR`` -- value of environment variable ``VAR`` (empty string if unset); truthy when non-empty
- ``env['VAR']`` -- same as ``env.VAR``
- ``factor.NAME`` -- ``True`` if ``NAME`` is a factor in the environment name or platform; ``False`` otherwise
- ``factor['NAME']`` -- same as ``factor.NAME``, for names that aren't valid Python identifiers (e.g. ``3.14``)
- ``env_name`` -- the full environment name as a string
- ``==``, ``!=`` -- string comparison
- ``and``, ``or``, ``not`` -- boolean logic
- ``'string'`` -- string literal

**********
 INI only
**********

These additional rules are active for native INI configuration.

The value for each setting in an INI configuration will be transformed according to the :ref:`Substitutions
<substitution>` section.

Substitution for values from other sections
===========================================

.. versionadded:: 1.4

Values from other sections can be referred to via:

::

    {[sectionname]valuename}

which you can use to avoid repetition of config values. You can put default values in one section and reference them in
others to avoid repeating the same values:

.. code-block:: ini

    [base]
    deps =
        pytest
        mock
        pytest-xdist

    [testenv:dulwich]
    deps =
        dulwich
        {[base]deps}

    [testenv:mercurial]
    deps =
        mercurial
        {[base]deps}

.. _conditional-settings:

Conditional settings
====================

- Configurations may be set conditionally within the ``tox.ini`` file. If a line starts with an environment name or
  names, separated by a comma, followed by ``:`` the configuration will only be used if the environment name(s) matches
  the executed tox environment. For example:

  .. code-block:: ini

      [testenv]
      deps =
         pip
         format: black
         py310,py39: pytest

  Here pip will be always installed as the configuration value is not conditional. black is only used for the ``format``
  environment, while ``pytest`` is only installed for the ``3.10`` and ``3.9`` environments.

- **Negative factors**: prefixing a factor name with ``!`` inverts the match -- the line is included only when the
  factor is *not* present in the environment name:

  .. code-block:: ini

      [testenv]
      deps =
          !lint: pytest
          !lint: coverage
          lint: ruff

  Here ``pytest`` and ``coverage`` are installed for every environment *except* ``lint``, while ``ruff`` is only
  installed for ``lint``.

- **Multi-factor conditions with negation**: you can combine positive and negative factors:

  .. code-block:: ini

      [testenv]
      deps =
          # installed only when both "django" and "mysql" factors are present
          django-mysql: PyMySQL
          # installed for all envs except those with the "slow" factor
          !slow: pytest-timeout
          # installed when either "3.12" or "3.13" factor is present, but not "minimal"
          !minimal-3.12,!minimal-3.13: hypothesis

- **Factor-conditional commands**: factor conditions work in any multi-line setting, not just ``deps``:

  .. code-block:: ini

      [testenv]
      commands =
          pytest tests
          coverage: coverage report --fail-under=80

  The ``coverage report`` command only runs in environments whose name contains the ``coverage`` factor (e.g.
  ``3.13-coverage``).

- **Default fallback**: when *all* lines in a setting are conditional and none match the current environment, the
  setting falls back to its default value. For example:

  .. code-block:: ini

      [testenv]
      base_python =
          py312: python3.12
          py313: python3.13

  If you run an environment named ``lint`` (which contains neither the ``py312`` nor ``py313`` factor), ``base_python``
  falls back to the default -- derived from the environment name -- rather than becoming an empty string. This applies
  to any configuration key, not just ``base_python``.

.. _generative-environment-list:

Generative environment list
===========================

If you have a large matrix of dependencies, python versions and/or environments you can use a generative :ref:`env_list`
and conditional settings to express that in a concise form:

.. tab:: TOML

    .. code-block:: toml

        env_list = [
            "lint",
            { product = [
                { prefix = "py3", start = 9, stop = 11 },
                ["django41", "django40"],
                ["sqlite", "mysql"],
            ] },
        ]

        [env_run_base]
        deps = [
            { replace = "if", condition = "factor.django41", then = ["Django>=4.1,<4.2"], extend = true },
            { replace = "if", condition = "factor.django40", then = ["Django>=4.0,<4.1"], extend = true },
            { replace = "if", condition = "factor.py311 and factor.mysql", then = ["PyMySQL"], extend = true },
            { replace = "if", condition = "factor.py311 or factor.py310", then = ["urllib3"], extend = true },
            { replace = "if", condition = "(factor.py311 or factor.py310) and factor.sqlite", then = ["mock"], extend = true },
        ]

.. tab:: INI

    .. code-block:: ini

        [tox]
        env_list = py3{9-11}-django{41,40}-{sqlite,mysql}

        [testenv]
        deps =
            django41: Django>=4.1,<4.2
            django40: Django>=4.0,<4.1
            py311-mysql: PyMySQL
            py311,py310: urllib3
            py{311,310}-sqlite: mock

This will generate the following tox environments (plus ``lint``):

.. code-block:: shell

    > tox l
    default environments:
    py39-django41-sqlite  -> [no description]
    py39-django41-mysql   -> [no description]
    py39-django40-sqlite  -> [no description]
    py39-django40-mysql   -> [no description]
    py310-django41-sqlite -> [no description]
    py310-django41-mysql  -> [no description]
    py310-django40-sqlite -> [no description]
    py310-django40-mysql  -> [no description]
    py311-django41-sqlite -> [no description]
    py311-django41-mysql  -> [no description]
    py311-django40-sqlite -> [no description]
    py311-django40-mysql  -> [no description]

INI expansion syntax
--------------------

Both enumerations (``{1,2,3}``) and numerical ranges (``{1-3}``) are supported, and can be mixed together:

.. code-block:: ini

    [tox]
    env_list = py3{8-10, 11, 13-14}

    [testenv]
    deps =
        py{310,311-314}: urllib3
    setenv =
        py{310,311-314}: FOO=bar

will create the following envs:

.. code-block:: shell

    > tox l
    default environments:
    py38  -> [no description]
    py39  -> [no description]
    py310 -> [no description]
    py311 -> [no description]
    py313 -> [no description]
    py314 -> [no description]

Negative ranges will also be expanded (``{3-1}`` -> ``{3,2,1}``). Non-numerical open ranges such as ``{a-}`` and
``{-b}`` will not be expanded.

Open-ended numerical ranges use bounds derived from the `supported CPython versions
<https://devguide.python.org/versions/>`_ at the time of the tox release:

- ``{10-}`` expands up to the latest supported CPython minor version (currently **14**)
- ``{-13}`` expands down from the oldest supported CPython minor version (currently **10**)

For example, ``py3{10-}`` is equivalent to ``py3{10,11,12,13,14}`` and ``py3{-13}`` is equivalent to
``py3{10,11,12,13}``. These bounds are updated with each tox release as new CPython versions become supported or old
ones reach end-of-life.

.. caution::

    Be conscious of the number of significant digits in your range endpoints. A range like ``py{39-314}`` will not do
    what you may expect. (It expands to 275 environment names, ``py39``, ``py40``, ``py41`` … ``py314``.) Instead, use
    ``py3{9-14}``.

TOML product syntax
-------------------

TOML uses a ``product`` dict instead of curly-brace expansion. Each factor group is an array of strings or a range dict.
The Cartesian product of all groups is computed and each combination is joined with ``-``.

Range dicts accept ``prefix``, ``start``, and ``stop``. Omit ``stop`` to expand up to the latest supported CPython minor
version (currently **14**), or omit ``start`` to expand down from the oldest (currently **10**):

.. code-block:: toml

    env_list = [
        { product = [{ prefix = "py3", start = 10 }, ["django42"]] },
    ]

The range ``{ prefix = "py3", start = 10 }`` is equivalent to ``py3{10-}`` in INI.

An ``exclude`` key removes specific combinations from the product -- a capability not available in INI:

.. code-block:: toml

    env_list = [
        { product = [["py312", "py313"], ["django42", "django50"]], exclude = ["py312-django50"] },
    ]

Generative section names
========================

Suppose you have some binary packages, and need to run tests both in 32 and 64 bits. You also want an environment to
create your virtual env for the developers. This also supports ranges in the same way as generative environment lists.

.. tab:: INI

    .. code-block:: ini

        [testenv]
        base_python =
            py311-x86: python3.11-32
            py311-x64: python3.11-64
        commands = pytest

        [testenv:py311-{x86,x64}-venv]
        envdir =
            x86: .venv-x86
            x64: .venv-x64

    .. code-block:: shell

        > tox l
        default environments:
        py          -> [no description]

        additional environments:
        py311-x86-venv -> [no description]
        py311-x64-venv -> [no description]

.. tab:: TOML

    TOML does not support generative section names. Use :ref:`env_base <env-base-templates>` templates instead:

    .. code-block:: toml

        [env_base.py311-venv]
        factors = [["x86", "x64"]]
        base_python = { replace = "if", condition = "factor.x86", then = "python3.11-32", "else" = "python3.11-64" }
        env_dir = { replace = "if", condition = "factor.x86", then = ".venv-x86", "else" = ".venv-x64" }
        commands = [["pytest"]]

    This generates ``py311-venv-x86`` and ``py311-venv-x64``, equivalent to the INI generative section.

.. _substitution:

***************
 Substitutions
***************

**Value substitution** operates through the ``{...}`` string-substitution pattern. The string inside the curly braces
may reference a global or per-environment config key as described above.

In substitutions, the backslash character ``\`` will act as an escape when preceding ``{``, ``}``, ``:``, ``[``, or
``]``, otherwise the backslash will be reproduced literally:

.. tab:: TOML

    .. code-block:: toml

        commands = [
          ["python", "-c", 'print("\{posargs} = \{}".format("{posargs}"))'],
          ["python", "-c", 'print("host: \{}".format("{env:HOSTNAME:host\: not set}")'],
        ]

.. tab:: INI

    .. code-block:: ini

        commands =
          python -c 'print("\{posargs} = \{}".format("{posargs}"))'
          python -c 'print("host: \{}".format("{env:HOSTNAME:host\: not set}")'

Note that any backslashes remaining after substitution may be processed by ``shlex`` during command parsing. On POSIX
platforms, the backslash will escape any following character; on windows, the backslash will escape any following quote,
whitespace, or backslash character (since it normally acts as a path delimiter).

Special substitutions that accept additional colon-delimited ``:`` parameters cannot have a space after the ``:`` at the
beginning of line (e.g. ``{posargs: magic}`` would be parsed as factorial ``{posargs``, having value magic).

.. _environment variable substitutions:

Environment variable substitutions
==================================

If you specify a substitution string like this:

::

    {env:KEY}

then the value will be retrieved as ``os.environ['KEY']`` and replaced with an empty string if the environment variable
does not exist.

Environment variable substitutions with default values
======================================================

If you specify a substitution string like this:

::

    {env:KEY:DEFAULTVALUE}

then the value will be retrieved as ``os.environ['KEY']`` and replaced with DEFAULTVALUE if the environment variable
does not exist.

If you specify a substitution string like this:

::

    {env:KEY:}

then the value will be retrieved as ``os.environ['KEY']`` and replaced with an empty string if the environment variable
does not exist.

Substitutions can also be nested. In that case they are expanded starting from the innermost expression:

::

    {env:KEY:{env:DEFAULT_OF_KEY}}

the above example is roughly equivalent to ``os.environ.get('KEY', os.environ['DEFAULT_OF_KEY'])``

Interactive shell substitution
==============================

.. versionadded:: 3.4.0

It's possible to inject a config value only when tox is running in interactive shell (standard input):

::

    {tty:ON_VALUE:OFF_VALUE}

The first value is the value to inject when the interactive terminal is available, the second value is the value to use
when it's not (optional). A good use case for this is e.g. passing in the ``--pdb`` flag for pytest.

.. _command positional substitution:

.. _positional substitution:

Substitutions for positional arguments in commands
==================================================

.. versionadded:: 1.0

If you specify a substitution string like this:

::

    {posargs:DEFAULTS}

then the value will be replaced with positional arguments as provided to the tox command:

::

    tox arg1 arg2

In this instance, the positional argument portion will be replaced with ``arg1 arg2``. If no positional arguments were
specified, the value of DEFAULTS will be used instead. If DEFAULTS contains other substitution strings, such as
``{env:*}``, they will be interpreted.,

Use a double ``--`` if you also want to pass options to an underlying test command, for example:

::

    tox run -e 3.14 -- --opt1 ARG1

will make the ``--opt1 ARG1`` appear in all test commands where ``[]`` or ``{posargs}`` was specified. By default (see
``args_are_paths`` setting), ``tox`` rewrites each positional argument if it is a relative path and exists on the
filesystem to become a path relative to the ``changedir`` setting.

.. _glob substitution:

Glob pattern substitution
=========================

.. versionadded:: 4.40

You can expand glob/wildcard patterns to matching file paths:

::

    {glob:PATTERN}

Matches are sorted and returned as a space-separated string. If no files match, the result is an empty string. You can
provide a default value for when no files match:

::

    {glob:PATTERN:DEFAULT}

Relative patterns are resolved against ``tox_root``. Use ``**`` for recursive matching across directories.

.. tab:: TOML

    .. code-block:: toml

        [env.A]
        commands = [["twine", "upload", "{glob:dist/*.whl}"]]

    Or using the TOML dict syntax (see :ref:`pyproject-toml-native`):

    .. code-block:: toml

        [env.A]
        commands = [["twine", "upload", { replace = "glob", pattern = "dist/*.whl", extend = true }]]

.. tab:: INI

    .. code-block:: ini

        [testenv]
        commands = twine upload {glob:dist/*.whl}
        deps = {glob:requirements/*.txt:requirements.txt}

Other substitutions
===================

- ``{:}`` -- replaced with ``os.pathsep`` (``:`` on POSIX, ``;`` on Windows). Useful for building ``PATH``-like values:
  ``set_env = PYTHONPATH={tox_root}/src{:}{tox_root}/lib``.
- ``{/}`` -- replaced with ``os.sep`` (``/`` on POSIX, ``\`` on Windows). Useful for cross-platform paths: ``commands =
  pytest {tox_root}{/}tests{/}unit``.

.. _substitution-reference:

Substitution quick reference
============================

The following table lists all available substitution variables. These can be used as inline replacement objects in TOML
or via ``{name}`` in INI.

.. list-table::
    :widths: 30 70
    :header-rows: 1

    - - Substitution
      - Description
    - - ``{tox_root}`` / ``{toxinidir}``
      - The directory where the configuration file is located (project root).
    - - ``{work_dir}`` / ``{toxworkdir}``
      - The tox working directory (default: ``{tox_root}/.tox``).
    - - ``{temp_dir}``
      - Temporary directory for tox (default: ``{work_dir}/.tmp``).
    - - ``{env_name}`` / ``{envname}``
      - Name of the current tox environment (e.g. ``3.13``, ``lint``).
    - - ``{env_dir}`` / ``{envdir}``
      - Directory of the current environment (default: ``{work_dir}/{env_name}``).
    - - ``{env_tmp_dir}`` / ``{envtmpdir}``
      - Temporary directory for the current environment (default: ``{env_dir}/tmp``).
    - - ``{env_log_dir}`` / ``{envlogdir}``
      - Log directory for the current environment (default: ``{env_dir}/log``).
    - - ``{env_bin_dir}`` / ``{envbindir}``
      - Binary directory of the virtual environment (e.g. ``{env_dir}/bin``).
    - - ``{env_python}`` / ``{envpython}``
      - Path to the Python executable in the virtual environment.
    - - ``{env_site_packages_dir}`` / ``{envsitepackagesdir}``
      - Pure-python site-packages directory (purelib) of the virtual environment.
    - - ``{env_site_packages_dir_plat}`` / ``{envsitepackagesdir_plat}``
      - Platform-specific site-packages directory (platlib) of the virtual environment.
    - - ``{base_python}`` / ``{basepython}``
      - The configured base Python interpreter.
    - - ``{py_dot_ver}``
      - Major.Minor version of the environment Python (e.g. ``3.14``).
    - - ``{py_impl}``
      - Python implementation name in lowercase (e.g. ``cpython``, ``pypy``).
    - - ``{py_free_threaded}``
      - ``True`` if the environment Python is a free-threaded build, else ``False``.
    - - ``{env:KEY}`` / ``{env:KEY:DEFAULT}``
      - Value of environment variable ``KEY``, with optional default.
    - - ``{posargs}`` / ``{posargs:DEFAULTS}``
      - Positional arguments passed after ``--``, with optional defaults.
    - - ``{tty:ON:OFF}``
      - ``ON`` value when running in an interactive terminal, ``OFF`` otherwise.
    - - ``{glob:PATTERN}`` / ``{glob:PATTERN:DEFAULT}``
      - Expand glob pattern to matching file paths (space-separated, sorted). Relative paths resolve against
        ``tox_root``.
    - - ``{/}``
      - OS path separator (``/`` or ``\``).
    - - ``{:}``
      - OS path list separator (``:`` or ``;``).
    - - ``{[section]key}`` *(INI only)*
      - Value of ``key`` from ``[section]`` (cross-section reference).

For TOML-specific replacement syntax (``replace = "ref"``, ``replace = "posargs"``, ``replace = "env"``, ``replace =
"glob"``, ``replace = "if"``), see :ref:`pyproject-toml-native`.
