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 = py26,py27
deps=pytest # or 'nose' or ...
commands=pytest  # or 'nosetests' or ...

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 py26

you can run restrict the test run to the python2.6 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.

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 = -rrequirements.txt -cconstraints.txt

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}/contrains.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 specificied 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        # comes from standard PyPI
    :DEV: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 =

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 as 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 better see about integrating 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{26,27,33}-django{15,16}-{sqlite,mysql}

deps =
    django15: Django>=1.5,<1.6
    django16: Django>=1.6,<1.7
    py33-mysql: PyMySQL     ; use if both py33 and mysql are in an env name
    py26,py27: urllib3      ; use if any of py26 or py27 are in an env name
    py{26,27}-sqlite: mock  ; mocking sqlite in python 2.x