.. _getting_started:

#################
 Getting Started
#################

This tutorial walks you through creating your first tox project from scratch. By the end, you will have a working tox
configuration that runs tests and linting across multiple Python versions.

***************
 Prerequisites
***************

Before starting, make sure you have:

- Python 3.10 or later installed
- tox installed (see :doc:`../how-to/install`)
- A Python project you want to test (or follow along to create one)

Verify tox is available:

.. code-block:: bash

    tox --version

***********************************
 Creating your first configuration
***********************************

tox needs a configuration file where you define what tools to run and how to set up environments for them. tox supports
two configuration formats: TOML and INI. **TOML is the recommended format for new projects** -- it is more robust, has
proper type support, and avoids ambiguities inherent in INI parsing. INI remains supported for existing projects.

Create a ``tox.toml`` (or ``tox.ini``) at the root of your project:

.. tab:: TOML

    .. code-block:: toml

         env_list = ["3.13", "3.12", "lint"]

         [env_run_base]
         description = "run the test suite with pytest"
         deps = [
             "pytest>=8",
         ]
         commands = [["pytest", { replace = "posargs", default = ["tests"], extend = true }]]

         [env.lint]
         description = "run linters"
         skip_install = true
         deps = ["ruff"]
         commands = [["ruff", "check", { replace = "posargs", default = ["."], extend = true }]]

.. tab:: INI

    .. code-block:: ini

         [tox]
         env_list = 3.13, 3.12, lint

         [testenv]
         description = run the test suite with pytest
         deps =
             pytest>=8
         commands =
             pytest {posargs:tests}

         [testenv:lint]
         description = run linters
         skip_install = true
         deps =
             ruff
         commands = ruff check {posargs:.}

.. tip::

    You can also generate a ``tox.ini`` file automatically by running ``tox quickstart`` and answering a few questions.

*********************************
 Understanding the configuration
*********************************

The configuration has two parts: **core settings** and **environment settings**.

Core settings
=============

Core settings affect all environments or configure how tox itself behaves. They live at the root level in ``tox.toml``
(or under the ``[tox]`` section in ``tox.ini``).

.. tab:: TOML

    .. code-block:: toml

       env_list = ["3.13", "3.12", "lint"]

.. tab:: INI

    .. code-block:: ini

       [tox]
       env_list = 3.13, 3.12, lint

The :ref:`env_list` setting defines which environments run by default when you invoke ``tox`` without specifying any.
Both formats support generating environment matrices from factor combinations — INI uses curly-brace expansion
(``3.{10-}``), while TOML composes from structured dicts. A single axis is a bare range dict (``{ prefix = "3.", start =
10 }``); multi-dimensional matrices use a ``product`` dict. See :ref:`generative-environment-list` for details. For the
full list of core options, see :ref:`conf-core`.

Environment settings
====================

Each tox environment has its own configuration. Settings defined at the base level (``env_run_base`` in TOML,
``testenv`` in INI) are inherited by all environments unless overridden. Individual environments are configured under
``env.<name>`` in TOML or ``testenv:<name>`` in INI.

.. tab:: TOML

    .. code-block:: toml

         [env_run_base]
         description = "run the test suite with pytest"
         deps = ["pytest>=8"]
         commands = [["pytest", { replace = "posargs", default = ["tests"], extend = true }]]

         [env.lint]
         description = "run linters"
         skip_install = true
         deps = ["ruff"]
         commands = [["ruff", "check", "."]]

.. tab:: INI

    .. code-block:: ini

         [testenv]
         description = run the test suite with pytest
         deps =
             pytest>=8
         commands =
             pytest {posargs:tests}

         [testenv:lint]
         description = run linters
         skip_install = true
         deps =
             ruff
         commands = ruff check .

Here the ``lint`` environment overrides the base settings entirely, while ``3.13`` and ``3.12`` inherit from the base.

.. tip::

    Options must go in the correct section — placing a core option in an environment section (or vice versa) silently
    has no effect. Run ``tox run -v`` or ``tox config`` to check for misplaced keys.

Environment names and Python versions
=====================================

Environment names can consist of alphanumeric characters, dashes, and dots. Names are split on dashes into **factors**
-- for example ``py311-django42`` splits into factors ``py311`` and ``django42``. Additionally, the current platform
(like ``linux``, ``darwin``, ``win32``) is automatically available as an implicit factor for conditional configuration.

tox recognizes certain naming patterns and automatically sets the Python interpreter:

- ``N.M``: CPython N.M (e.g. ``3.13``) -- **preferred**
- ``pyNM`` or ``pyN.M``: CPython N.M (e.g. ``py313`` or ``py3.13``) -- legacy, still supported
- ``pypyNM``: PyPy N.M
- ``cpythonNM``: CPython N.M
- ``graalpyNM``: GraalPy N.M

Prefer the ``N.M`` form (e.g. ``3.14``) over ``pyNMM`` (e.g. ``py314``). The dotted form is unambiguous, reads more
naturally in environment lists and CI output, and avoids confusion for Python versions >= 3.10 where the concatenated
digits become three characters.

.. note::

    Version-number factors like ``3.14`` can be checked in conditional expressions using subscript syntax:
    ``factor['3.14']`` (the dot-syntax ``factor.3.14`` would be a syntax error). See :ref:`conditional-value-reference`
    for details.

If the name doesn't match any pattern, tox uses the same Python as the one tox is installed into (this is the case for
``lint`` in our example). To override this fallback, set :ref:`default_base_python`:

.. code-block:: toml

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

This pins a default Python version for environments without a Python factor, improving reproducibility across machines
with different system Pythons.

.. tip::

    If your project uses :PEP:`751` lock files (``pylock.toml``), you can install locked dependencies via :ref:`pylock`
    instead of listing packages in ``deps``.

For the full list of environment options, see :ref:`conf-testenv`.

Scaling to multiple Python versions
===================================

When your test matrix grows beyond a few environments, use ``env_base`` sections to define named templates that generate
environments from factor combinations:

.. 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``, each inheriting deps and commands from the template. The template itself
inherits from ``env_run_base``, so global defaults still apply. See :ref:`env-base-templates` for details.

***************************
 Running your environments
***************************

Run all default environments (those listed in :ref:`env_list`):

.. code-block:: bash

    tox

Run a specific environment:

.. code-block:: bash

    tox run -e lint

Run multiple environments:

.. code-block:: bash

    tox run -e 3.13,lint

Pass extra arguments to the underlying tool using ``--``:

.. code-block:: bash

    # Run pytest in verbose mode
    tox run -e 3.13 -- -v

    # Run ruff on a specific file
    tox run -e lint -- src/mymodule.py

The ``{ replace = "posargs" }`` in TOML (or ``{posargs}`` in INI) is a placeholder that gets replaced by whatever you
pass after ``--``.

**************************
 Understanding the output
**************************

On the first run, tox creates virtual environments and installs dependencies. Subsequent runs reuse existing
environments unless dependencies change:

.. code-block:: bash

    $ tox run -e 3.13,lint
    3.13: install_deps> python -m pip install 'pytest>=8'
    3.13: commands[0]> pytest tests
    ========================= 3 passed in 0.12s =========================
    3.13: OK ✔ in 5.43s
    lint: install_deps> python -m pip install ruff
    lint: commands[0]> ruff check .
    All checks passed!
    lint: OK ✔ in 2.11s

      3.13: OK (5.43=setup[3.21]+cmd[2.22] seconds)
      lint: OK (2.11=setup[1.05]+cmd[1.06] seconds)
      congratulations :)

tox will automatically detect changes to your dependencies and recreate environments when needed. You can force a full
recreation with the ``-r`` flag:

.. code-block:: bash

    tox run -e 3.13 -r

If tools inside the environment maintain their own caches (e.g. pre-commit), you can use :ref:`recreate_commands` to
clean them before the environment directory is removed. See :ref:`howto_clean_caches` for details.

If you want to rerun tests without reinstalling dependencies or the package (e.g. when working offline or when nothing
has changed), use ``--skip-env-install``:

.. code-block:: bash

    tox run -e 3.13 --skip-env-install

********************************
 Listing available environments
********************************

See all configured environments and their descriptions:

.. code-block:: bash

    $ tox list
    default environments:
    3.13 -> run the test suite with pytest
    3.12 -> run the test suite with pytest
    lint -> run linters

**************************
 Inspecting configuration
**************************

View the resolved configuration for an environment:

.. code-block:: bash

    tox config -e 3.13 -k deps commands

The output format can be changed with ``--format`` and written to a file with ``-o``:

.. code-block:: bash

    tox config -e 3.13 --format json -o config.json
    tox config -e 3.13 --format toml -o config.toml

This is useful for debugging configuration issues and for programmatic consumption.

************
 Next steps
************

Now that you have a working tox setup, explore these topics:

- :doc:`../explanation` -- understand how tox works (parallel mode, packaging, auto-provisioning)
- :doc:`../how-to/usage` -- practical recipes for common tasks (including testing across old and new Python versions
  with :ref:`virtualenv_spec`)
- :ref:`configuration` -- full configuration reference
- :ref:`cli` -- complete CLI reference
- :ref:`howto_pep723` -- run standalone scripts with inline dependencies (:PEP:`723`)
