tox configuration specification

tox.ini files uses the standard ConfigParser “ini-style” format. Below you find the specification, but you might want to skim some tox configuration and usage examples first and use this page as a reference.

tox global settings

List of optional global options:

# minimally required tox version
# tox working directory, defaults to {toxinidir}/.tox
# defaults to {toxinidir}
# defaults to {toxworkdir}/dist
# (DEPRECATED) defaults to {homedir}/.tox/distshare
# defaults to the list of all environments
# bool: defaults to False

tox autodetects if it is running in a Jenkins context (by checking for existence of the JENKINS_URL environment variable) and will first lookup global tox settings in this section:

commands = ...  # override [tox] settings for the jenkins context
# note: for jenkins distshare defaults to ``{toxworkdir}/distshare`` (DEPRECATED)

New in version 1.7.2.

Setting this to True is equivalent of passing the --skip-missing-interpreters command line option, and will force tox to return success even if some of the specified environments were missing. This is useful for some CI systems or 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 invokation. Default: False


Determining the environment list that tox is to operate on happens in this order (if any is found, no further lookups are made):

  • command line option -eENVLIST
  • environment variable TOXENV
  • tox.ini file’s envlist

New in version 3.1.0.

If True, basepython settings that conflict with the Python variant for environments using default factors, such as py27 or py35, will be ignored. This allows you to configure basepython in the global testenv without affecting these factors. If False, the default, a warning will be emitted if a conflict is identified. In a future version of tox, this warning will become an error.


New in version 3.2.0.

Specify python packages that need to exist alongside the tox installation for the tox build to be able to start. Use this to specify plugin requirements and build dependencies.

requires = setuptools >= 30.0.0

New in version 3.3.0.

Activate isolated build environment. tox will use a virtual environment to build a source distribution from the source tree. For build tools and arguments use the pyproject.toml file as specified in PEP-517 and PEP-518. To specify the virtual environment Python version define use the isolated_build_env config section.


New in version 3.3.0.

Name of the virtual environment used to create a source distribution from the source tree. By default ``.package`` is used.

Virtualenv test environment settings

Test environments are defined by a:

commands = ...

section. The NAME will be the name of the virtual environment. Defaults for each setting in this section are looked up in the:

commands = ...

testenvironment default section.

Complete list of settings that you can put into testenv* sections:


Name or path to a Python interpreter which will be used for creating the virtual environment; if the environment name contains a default factor, this value will be ignored. default: interpreter used for tox invocation.

Changed in version 3.1: Environments that use a default factor now ignore this value, defaulting to the interpreter defined for that factor.


The commands to be called for testing. Each command is defined by one or more lines; a command can have multiple lines if a line ends with the \ character in which case the subsequent line will be appended (and may contain another \ character …). For eventually performing a call to subprocess.Popen(args, ...) args are determined by splitting the whole command by whitespace.

To execute commands that can fail, they can be prefixed with a dash (-). For these commands the exitcode is ignored. In this example ls -la will always be executed although cat might return 1 for a not existing file:

commands =
    - cat non-existing-file.txt
    - ls -la

This is similar to make recipe lines.


New in version 1.6.

The install_command setting is used for installing packages into the virtual environment; both the package under test and its dependencies (defined with deps). Must contain the substitution key {packages} which will be replaced by the packages to install. You should also accept {opts} if you are using pip – it will contain index server options such as --pre (configured as pip_pre) and potentially index-options from the deprecated indexserver option.


pip install {opts} {packages}

New in version 2.4.

The list_dependencies_command setting is used for listing the packages installed into the virtual environment.


pip freeze

New in version 2.0.

If True, a non-zero exit code from one command will be ignored and further commands will be executed (which was the default behavior in tox < 2.0). If False (the default), then a non-zero exit code from one command will abort execution of commands for that environment.

It may be helpful to note that this setting is analogous to the -i or ignore-errors option of GNU Make. A similar name was chosen to reflect the similarity in function.

Note that in tox 2.0, the default behavior of tox with respect to treating errors from commands changed. tox < 2.0 would ignore errors by default. tox >= 2.0 will abort on an error by default, which is safer and more typical of CI and command execution tools, as it doesn’t make sense to run tests if installing some prerequisite failed and it doesn’t make sense to try to deploy if tests failed.


New in version 1.9.

If True, adds --pre to the opts passed to install_command. If install_command uses pip, this will cause it to install the latest available pre-release of any dependencies without a specified version. If False (the default), pip will only install final releases of unpinned dependencies.

Passing the --pre command-line option to tox will force this to True for all testenvs.

Don’t set this option if your install_command does not use pip.


each line specifies a command name (in glob-style pattern format) which can be used in the commands section without triggering a “not installed in virtualenv” warning. Example: if you use the unix make for running tests you can list whitelist_externals=make or whitelist_externals=/usr/bin/make if you want more precision. If you don’t want tox to issue a warning in any case, just use whitelist_externals=* which will match all commands (not recommended).


change to this working directory when executing the test command.

default: {toxinidir}


Test-specific dependencies - to be installed into the environment prior to project package installation. Each line defines a dependency, which will be passed to the installer command for processing (see indexserver). Each line specifies a file, a URL or a package name. You can additionally specify an indexserver to use for installing this dependency but this functionality is deprecated since tox-2.3. All derived dependencies (deps required by the dep) will then be retrieved from the specified indexserver:

indexserver =
    myindexserver =

deps = :myindexserver:pkg

(Experimentally introduced in 1.6.1) all installer commands are executed using the {toxinidir} as the current working directory.


New in version 2.0.

A testenv can define a new platform setting as a regular expression. If a non-empty expression is defined and does not match against the sys.platform string the test environment will be skipped.


New in version 0.9.

Each line contains a NAME=VALUE environment variable setting which will be used for all test command invocations as well as for installing the sdist package into a virtual environment.

Notice that when updating a path variable, you can consider the use of variable substitution for the current value and to handle path separator.

setenv   =
    PYTHONPATH = {env:PYTHONPATH}{:}{toxinidir}

New in version 2.0.

A list of wildcard environment variable names which shall be copied from the tox invocation environment to the test environment when executing test commands. If a specified environment variable doesn’t exist in the tox invocation environment it is ignored. You can use * and ? to match multiple environment variables with one name.

Some variables are always passed through to ensure the basic functionality of standard library functions or tooling like pip:

  • passed through on all platforms: PATH, LANG, LANGUAGE, LD_LIBRARY_PATH, PIP_INDEX_URL
  • Others (e.g. UNIX, macOS): TMPDIR

You can override these variables with the setenv option.

If defined the TOX_TESTENV_PASSENV environment variable (in the tox invocation environment) can define additional space-separated variable names that are to be passed down to the test command environment.

Changed in version 2.7: PYTHONPATH will be passed down if explicitly defined. If PYTHONPATH exists in the host environment but is not declared in passenv a warning will be emitted.


Always recreate virtual environment if this option is True.


IGNORED – Since pip-8 has caching by default this option is now ignored. Please remove it from your configs as a future tox version might bark on it.


Set to True if you want to create virtual environments that also have access to globally installed packages.

default: False, meaning that virtualenvs will be created without inheriting the global site packages.


Set to True if you want virtualenv to always copy files rather than symlinking.

This is useful for situations where hardlinks don’t work (e.g. running in VMS with Windows guests).

default: False, meaning that virtualenvs will make use of symbolic links.


Treat positional arguments passed to tox as file system paths and - if they exist on the filesystem - rewrite them according to the changedir.

default: True (due to the exists-on-filesystem check it’s usually safe to try rewriting).


Defines a temporary directory for the virtualenv which will be cleared each time before the group of test commands is invoked.

default: {envdir}/tmp


Defines a directory for logging where tox will put logs of tool invocation.

default: {envdir}/log


New in version 0.9.

(DEPRECATED, will be removed in a future version) Multi-line name = URL definitions of python package servers. Dependencies can specify using a specified index server through the :indexservername:depname pattern. The default indexserver definition determines where unscoped dependencies and the sdist install installs from. Example:

indexserver =
    default =

will make tox install all dependencies from this PYPI index server (including when installing the project sdist package).


New in version 1.5.

User can set specific path for environment. If path would not be absolute it would be treated as relative to {toxinidir}.

default: {toxworkdir}/{envname}


New in version 1.6.

Install the current package in development mode with “ develop” instead of installing from the sdist package. (This uses pip’s -e option, so should be avoided if you’ve specified a custom install_command that does not support -e).

default: False


New in version 1.9.

Do not install the current package. This can be used when you need the virtualenv management but do not want to install the current package into that environment.

default: False


New in version 2.2.

If set to True a failing result of this testenv will not make tox fail, only a warning will be produced.

default: False


New in version 2.4.

A list of “extras” to be installed with the sdist or develop install. For example, extras = testing is equivalent to [testing] in a pip install command.


A short description of the environment, this will be used to explain the environment to the user upon listing environments for the command line with any level of verbosity higher than zero. default: empty string


Any key=value setting in an ini-file can make use of value substitution through the {...} string-substitution pattern.

You can escape curly braces with the \ character if you need them, for example:

commands = echo "\{posargs\}" = {posargs}

Globally available substitutions

the directory where tox.ini is located
the directory where virtual environments are created and sub directories for packaging reside.
the user-home directory path.
the directory where sdist-packages will be created in
(DEPRECATED) the directory where sdist-packages will be copied to so that they may be accessed by other processes or tox runs.
OS-specific path separator (: os *nix family, ; on Windows). May be used in setenv, when target variable is path variable (e.g. PATH or PYTHONPATH).

environment variable substitutions

If you specify a substitution string like this:


then the value will be retrieved as os.environ['KEY'] and raise an Error if the environment variable does not exist.

environment variable substitutions with default values

If you specify a substitution string like this:


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

If you specify a substitution string like this:


then the value will be retrieved as os.environ['KEY'] and replace 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:


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

substitutions for positional arguments in commands

New in version 1.0.

If you specify a substitution string like this:


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 -- --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.

Previous versions of tox supported the [.*] pattern to denote positional arguments with defaults. This format has been deprecated. Use {posargs:DEFAULTS} to specify those.

Substitution for values from other sections

New in version 1.4.

Values from other sections can be referred to via:


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:

deps =

deps =

deps =

Generating environments, conditional settings

New in version 1.8.

Suppose you want to test your package against python2.7, python3.6 and against several versions of a dependency, say Django 1.5 and Django 1.6. You can accomplish that by writing down 2*2 = 4 [testenv:*] sections and then listing all of them in envlist.

However, a better approach looks like this:

envlist = {py27,py36}-django{15,16}

deps =
    django15: Django>=1.5,<1.6
    django16: Django>=1.6,<1.7
    py36: unittest2
commands = pytest

This uses two new facilities of tox-1.8:

  • generative envlist declarations where each envname consists of environment parts or “factors”
  • “factor” specific settings

Let’s go through this step by step.

Generative envlist

envlist = {py36,py27}-django{15,16}

This is bash-style syntax and will create 2*2=4 environment names like this:


You can still list environments explicitly along with generated ones:

envlist = {py27,py36}-django{15,16}, docs, flake

Keep in mind that whitespace characters (except newline) within {} are stripped, so the following line defines the same environment names:

envlist = {py27,py36}-django{ 15, 16 }, docs, flake


To help with understanding how the variants will produce section values, you can ask tox to show their expansion with a new option:

$ tox -l

Factors and factor-conditional settings

Parts of an environment name delimited by hyphens are called factors and can be used to set values conditionally. In list settings such as deps or commands you can freely intermix optional lines with unconditional ones:

deps =
    django15: Django>=1.5,<1.6
    django16: Django>=1.6,<1.7
    py36: unittest2

Reading it line by line:

  • pytest will be included unconditionally,
  • Django>=1.5,<1.6 will be included for environments containing django15 factor,
  • Django>=1.6,<1.7 similarly depends on django16 factor,
  • unittest will be loaded for Python 3.6 environments.

tox provides a number of default factors corresponding to Python interpreter versions. The conditional setting above will lead to either python3.6 or python2.7 used as base python, e.g. python3.6 is selected if current environment contains py36 factor.


Configuring basepython for environments using default factors will result in a warning. Configure ignore_basepython_conflict if you wish to explicitly ignore these conflicts, allowing you to define a global basepython for all environments except those with default factors.

Complex factor conditions

Sometimes you need to specify the same line for several factors or create a special case for a combination of factors. Here is how you do it:

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

deps =
    py34-mysql: PyMySQL     ; use if both py34 and mysql are in the env name
    py27,py36: urllib3      ; use if either py36 or py27 are in the env name
    py{27,36}-sqlite: mock  ; mocking sqlite in python 2.x & 3.6
    !py34-sqlite: mock      ; mocking sqlite, except in python 3.4
    sqlite-!py34: mock      ; (same as the line above)

Take a look at the first deps line. It shows how you can special case something for a combination of factors, by just hyphenating the combining factors together. This particular line states that PyMySQL will be loaded for python 3.3, mysql environments, e.g. py34-django15-mysql and py34-django16-mysql.

The second line shows how you use the same setting for several factors - by listing them delimited by commas. It’s possible to list not only simple factors, but also their combinations like py27-sqlite,py36-sqlite.

The remaining lines all have the same effect and use conditions equivalent to py27-sqlite,py36-sqlite. They have all been added only to help demonstrate the following:

  • how factor expressions get expanded the same way as in envlist
  • how to use negated factor conditions by prefixing negated factors with !
  • that the order in which factors are hyphenated together does not matter


Factors don’t do substring matching against env name, instead every hyphenated expression is split by - and if ALL of its non-negated factors and NONE of its negated ones are also factors of an env then that condition is considered to hold for that env.

For example, environment py36-mysql-!dev:

  • would be matched by expressions py36, py36-mysql or mysql-py36,
  • but not py2, py36-sql or py36-mysql-dev.

Advanced settings

Handle interpreter directives with long lengths

For systems supporting executable text files (scripts with a shebang), the system will attempt to parse the interpreter directive to determine the program to execute on the target text file. When tox prepares a virtual environment in a file container which has a large length (e.x. using Jenkins Pipelines), the system might not be able to invoke shebang scripts which define interpreters beyond system limits (e.x. Linux as a limit of 128; BINPRM_BUF_SIZE). To workaround an environment which suffers from an interpreter directive limit, a user can bypass the system’s interpreter parser by defining the TOX_LIMITED_SHEBANG environment variable before invoking tox:


When the workaround is enabled, all tox-invoked text file executables will have their interpreter directive parsed by and explicitly executed by tox.

Other Rules and notes

  • path specifications: if a specified path is a relative path it will be considered as relative to the toxinidir, the directory where the configuration file resides.