Basic usage

a simple tox.ini / default environments

Put basic information about your project and the test environments you want your project to run in into a tox.ini file that should reside next to your file:

# content of: tox.ini , put in same dir as
envlist = py27,py36
# install testing framework
# ... or install anything else you might need here
deps = pytest
# run the tests
# ... or run any other command line tool you need to run here
commands = pytest

To sdist-package, install and test your project, you can now type at the command prompt:


This will sdist-package your current project, create two virtualenv Environments, install the sdist-package into the environments and run the specified command in each of them. With:

tox -e py36

you can run restrict the test run to the python3.6 environment.

Available “default” test environments names are:


The environment py uses the version of Python used to invoke tox.

However, you can also create your own test environment names, see some of the examples in examples.

pyproject.toml tox legacy ini

The tox configuration can also be in pyproject.toml (if you want to avoid an extra file).

Currently only the old format is supported via legacy_tox_ini, a native implementation is planned though.

requires = [ "setuptools >= 35.0.2", "wheel >= 0.29.0"]
build-backend = "setuptools.build_meta"

legacy_tox_ini = """
envlist = py27,py36

deps = pytest >= 3.0.0, <4
commands = pytest

Note that when you define a pyproject.toml you must define the build-requires section per PEP-518.

specifying a platform

New in version 2.0.

If you want to specify which platform(s) your test environment runs on you can set a platform regular expression like this:

platform = linux2|darwin

If the expression does not match against sys.platform the test environment will be skipped.

whitelisting non-virtualenv commands

New in version 1.5.

Sometimes you may want to use tools not contained in your virtualenv such as make, bash or others. To avoid warnings you can use the whitelist_externals testenv configuration:

# content of tox.ini
whitelist_externals = make

depending on requirements.txt or defining constraints

New in version 1.6.1.

(experimental) If you have a requirements.txt file or a constraints.txt file you can add it to your deps variable like this:

deps = -rrequirements.txt


deps = -cconstraints.txt


deps =

All installation commands are executed using {toxinidir} (the directory where tox.ini resides) as the current working directory. Therefore, the underlying pip installation will assume requirements.txt or constraints.txt to exist at {toxinidir}/requirements.txt or {toxinidir}/constraints.txt.

This is actually a side effect that all elements of the dependency list is directly passed to pip.

For more details on requirements.txt files or constraints.txt files please see:

using a different default PyPI url

New in version 0.9.

To install dependencies and packages from a different default PyPI server you can type interactively:

tox -i

This causes tox to install dependencies and the sdist install step to use the specified url as the index server.

You can cause the same effect by this tox.ini content:

indexserver =
    default =

installing dependencies from multiple PyPI servers

New in version 0.9.

You can instrument tox to install dependencies from different PyPI servers, example:

indexserver =
    DEV =

deps =
    # docutils will be installed directly from PyPI
    # mypackage will be installed from custom "DEV" PyPI url

This configuration will install docutils from the default Python PYPI server and will install the mypackage from our DEV indexserver, and the respective url. You can override config file settings from the command line like this:

tox -i DEV=  # changes :DEV: package URLs
tox -i      # changes default

further customizing installation

New in version 1.6.

By default tox uses pip to install packages, both the package-under-test and any dependencies you specify in tox.ini. You can fully customize tox’s install-command through the testenv-specific install_command=ARGV setting. For instance, to use pip’s --find-links and --no-index options to specify an alternative source for your dependencies:

install_command = pip install --pre --find-links --no-index {opts} {packages}

forcing re-creation of virtual environments

New in version 0.9.

To force tox to recreate a (particular) virtual environment:

tox --recreate -e py27

would trigger a complete reinstallation of the existing py27 environment (or create it afresh if it doesn’t exist).

passing down environment variables

New in version 2.0.

By default tox will only pass the PATH environment variable (and on windows SYSTEMROOT and PATHEXT) from the tox invocation to the test environments. If you want to pass down additional environment variables you can use the passenv option:

passenv = LANG

When your test commands execute they will execute with the same LANG setting as the one with which tox was invoked.

setting environment variables

New in version 1.0.

If you need to set an environment variable like PYTHONPATH you can use the setenv directive:

setenv = PYTHONPATH = {toxinidir}/subdir

When your test commands execute they will execute with a PYTHONPATH setting that will lead Python to also import from the subdir below the directory where your tox.ini file resides.

special handling of PYTHONHASHSEED

New in version 1.6.2.

By default, tox sets PYTHONHASHSEED for test commands to a random integer generated when tox is invoked. This mimics Python’s hash randomization enabled by default starting in Python 3.3. To aid in reproducing test failures, tox displays the value of PYTHONHASHSEED in the test output.

You can tell tox to use an explicit hash seed value via the --hashseed command-line option to tox. You can also override the hash seed value per test environment in tox.ini as follows:

setenv = PYTHONHASHSEED = 100

If you wish to disable this feature, you can pass the command line option --hashseed=noset when tox is invoked. You can also disable it from the tox.ini by setting PYTHONHASHSEED = 0 as described above.

Integration with “ test” command


Integrating tox with test is as of October 2016 discouraged as it breaks packaging/testing approaches used by downstream distributions which expect test to run tests with the invocation interpreter rather than setting up many virtualenvs and installing packages. If you need to define test, you can see how to integrate your eventual test runner with it, here is an example of test integration with pytest. As the python eco-system rather moves away from using as a tool entry point it’s maybe best to not go for any test integration.

Ignoring a command exit code

In some cases, you may want to ignore a command exit code. For example:

commands = coverage erase
       {envbindir}/python develop
       coverage run -p test
       coverage combine
       - coverage html
       {envbindir}/flake8 loads

By using the - prefix, similar to a make recipe line, you can ignore the exit code for that command.

Compressing dependency matrix

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

envlist = py{27,34,36}-django{15,16}-{sqlite,mysql}

deps =
    django15: Django>=1.5,<1.6
    django16: Django>=1.6,<1.7
    # use PyMySQL if factors "py34" and "mysql" are present in env name
    py34-mysql: PyMySQL
    # use urllib3 if any of "py36" or "py27" are present in env name
    py27,py36: urllib3
    # mocking sqlite on 2.7 and 3.6 if factor "sqlite" is present
    py{27,36}-sqlite: mock

Parallel mode

tox allows running environments in parallel:

  • Invoke by using the --parallel or -p flag. After the packaging phase completes tox will run in parallel processes tox environments (spins a new instance of the tox interpreter, but passes through all host flags and environment variables).

  • -p takes an argument specifying the degree of parallelization:

    • all to run all invoked environments in parallel,

    • auto to limit it to CPU count,

    • or pass an integer to set that limit.

  • Parallel mode displays a progress spinner while running tox environments in parallel, and reports outcome of these as soon as completed with a human readable duration timing attached.

  • Parallel mode by default shows output only of failed environments and ones marked as parallel_show_output =True.

  • There’s now a concept of dependency between environments (specified via depends), tox will re-order the environment list to be run to satisfy these dependencies (in sequential run too). Furthermore, in parallel mode, will only schedule a tox environment to run once all of its dependencies finished (independent of their outcome).


    depends does not pull in dependencies into the run target, for example if you select py27,py36,coverage via the -e tox will only run those three (even if coverage may specify as depends other targets too - such as py27, py35, py36, py37).

  • --parallel-live/-o allows showing the live output of the standard output and error, also turns off reporting described above.

  • Note: parallel evaluation disables standard input. Use non parallel invocation if you need standard input.

Example final output:

$ tox -e py27,py36,coverage -p all
✔ OK py36 in 9.533 seconds
✔ OK py27 in 9.96 seconds
✔ OK coverage in 2.0 seconds
___________________________ summary ______________________________________________________
  py27: commands succeeded
  py36: commands succeeded
  coverage: commands succeeded
  congratulations :)

Example progress bar, showing a rotating spinner, the number of environments running and their list (limited up to 120 characters):

[2] py27 | py36

tox auto-provisioning

In case the host tox does not satisfy either the minversion or the requires, tox will now automatically create a virtual environment under provision_tox_env that satisfies those constraints and delegate all calls to this meta environment. This should allow automatically satisfying constraints on your tox environment, given you have at least version 3.8.0 of tox.

For example given:

minversion = 3.10.0
requires = tox_venv >= 1.0.0

if the user runs it with tox 3.8.0 or later installed tox will automatically ensured that both the minimum version and requires constraints are satisfied, by creating a virtual environment under .tox folder, and then installing into it tox >= 3.10.0 and tox_venv >= 1.0.0. Afterwards all tox invocations are forwarded to the tox installed inside .tox\.tox folder (referred to as meta-tox or auto-provisioned tox).

This allows tox to automatically setup itself with all its plugins for the current project. If the host tox satisfies the constraints expressed with the requires and minversion no such provisioning is done (to avoid setup cost when it’s not explicitly needed).