tox configuration specification

configuration discovery

At the moment tox supports three configuration locations prioritized in the following order:

  1. pyproject.toml,
  2. tox.ini,
  3. setup.cfg.

As far as the configuration format at the moment we only support standard ConfigParser “ini-style” format (there is a plan to add a pure TOML one soon). tox.ini and setup.cfg are such files. Note that setup.cfg requires the content to be under the tox:tox section. pyproject.toml on the other hand is in TOML format. However, one can inline the ini-style format under the tool.tox.legacy_tox_ini key as a multi-line string.

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

tox global settings

Global settings are defined under the tox section as:

minversion = 3.4.0

Define the minimal tox version required to run; if the host tox is less than this the tool with exit with an error message indicating the user needs to upgrade tox.


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


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).


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


Indicates where the packaging root file exists (historically the for setuptools). This will be the working directory when performing the packaging.


Directory where the packaged source distribution should be put. Note this is cleaned at the start of every packaging invocation.


Do not build the package, but instead use the latest package available under this path. You can override it via the command line flag --installpkg.


Folder where the packaged source distribution will be moved, this is not cleaned between packaging invocations. On Jenkins (exists JENKINS_URL or HUDSON_URL environment variable) the default path is {toxworkdir}/distshare.

envlist(comma separated values)

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 3.4.0: What tox environments are ran 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.


New in version 1.7.2.

When skip missing interpreters is true 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 invocation. Setting it to config means that the value is read from the config file.


New in version 3.1.0.

tox allows setting the python version for an environment via the basepython setting. If that’s not set tox can set a default value from the environment name ( e.g. py37 implies Python 3.7). 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 a warning will be emitted whenever the environment name version does not matches up with this expectation. In a future version of tox, this warning will become an error.

Furthermore, we allow hard enforcing this rule (and bypassing the warning) by setting this flag to true. In such cases we ignore the basepython and instead always use the base python implied from the Python name. This allows you to configure basepython in the global testenv without affecting environments that have implied base python versions.

requires(LIST of PEP-508)

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 = tox-venv
           setuptools >= 30.0.0


tox does not install those required packages for you. tox only checks if the requirements are satisfied and crashes early with an helpful error rather then later in the process.


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.

Jenkins override

It is possible to override global settings inside a Jenkins instance ( detection is by checking for existence of the JENKINS_URL environment variable) by using the tox:jenkins section:

commands = ...  # override settings for the jenkins context

tox 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 = ...

testenv 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, 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) wil be used to automatically set one. E.g. py37 means python3.7, py3 means python3 and py means python.

Changed in version 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 ignore_basepython_conflict is set, the value is ignored and we force the basepython implied from the factor name.


The commands to be called for testing. Only execute if 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 (the bin folder within) is prepended to the os PATH, 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 basepython), and pip translates as the virtual environments pip.

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


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

install_command=python -m pip install {opts} {packages}(ARGV)

New in version 1.6.

Determines the command 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 package(s) 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.

list_dependencies_command=python -m pip freeze(ARGV)

New in version 2.4.

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


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, 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, 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.


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.


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).


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


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


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}.


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).


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.


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.


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.

description=no description(SINGLE-LINE-TEXT)

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.


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}

Note some substitutions (e.g. posargs, env) may have addition values attached to it, via the : character (e.g. posargs - default value, env - key). Such substitutions cannot have a space after the : character (e.g. {posargs: magic} while being at the start of a line inside the ini configuration (this would be parsed as factorial {posargs, having value magic).

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'])

interactive shell substitution

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


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. The later on is optional. A good use case for this is e.g. passing in the --pdb flag for pytest.

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 3.4, 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.

Factors and values substitution are compatible

It is possible to mix both values substitution and factor expressions. For example:

envlist = py27,py36,coverage

deps =
    coverage: coverage

deps =

With the previous configuration, it will install:

  • flake8 and pytest packages for py27 environment.
  • flake8 package for py36 environment.
  • flake8 and coverage packages for coverage environment.

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.

Injected environment variables

tox will inject the following environment variables that you can use to test that your command is running within tox:

New in version 3.4.

  • TOX_WORK_DIR env var is set to the tox work directory
  • TOX_ENV_NAME is set to the current running tox environment name
  • TOX_ENV_DIR is set to the current tox environments working dir.
note:this applies for all tox envs (isolated packaging too) and all external commands called (e.g. install command - pip).

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.



tox options

usage: tox [--version] [-h] [--help-ini] [-v] [-q] [--showconfig] [-l] [-a]
           [-c CONFIGFILE] [-e envlist] [--notest] [--sdistonly]
           [--parallel--safe-build] [--installpkg PATH] [--develop] [-i URL]
           [--pre] [-r] [--result-json PATH] [--hashseed SEED]
           [--force-dep REQ] [--sitepackages] [--alwayscopy]
           [--skip-missing-interpreters [val]] [--workdir PATH]
           [args [args ...]]

additional arguments available to command positional substitution


report version information to stdout.

-h, --help

show help about options

--help-ini, --hi

show help about ini-names


increase verbosity of reporting output.-vv mode turns off output redirection for package installation, above level two verbosity flags are passed through to pip (with two less level)


progressively silence reporting output.


show configuration information for all environments.

-l, --listenvs

show list of test environments (with description if verbose)

-a, --listenvs-all

show list of all defined environments (with description if verbose)

-c <configfile>

config file name or directory with ‘tox.ini’ file.

-e <envlist>

work against specified environments (ALL selects all).


skip invoking test commands.


only perform the sdist packaging activity.


(deprecated) ensure two tox builds can run in parallel (uses a lock file in the tox workdir with .lock extension)

--installpkg <path>

use specified package for installation into venv, instead of creating an sdist.


install package in the venv using ‘ develop’ via ‘pip -e .’

-i <url>, --index-url <url>

set indexserver url (if URL is of form name=url set the url for the ‘name’ indexserver, specifically)


install pre-releases and development versions of dependencies. This will pass the –pre option to install_command (pip by default).

-r, --recreate

force recreation of virtual environments

--result-json <path>

write a json file with detailed information about all commands and results involved.

--hashseed <seed>

set PYTHONHASHSEED to SEED before running commands. Defaults to a random integer in the range [1, 4294967295] ([1, 1024] on Windows). Passing ‘noset’ suppresses this behavior.

--force-dep <req>

Forces a certain version of one of the dependencies when configuring the virtual environment. REQ Examples ‘pytest<2.7’ or ‘django>=1.6’.


override sitepackages setting to True in all envs


override alwayscopy setting to True in all envs


don’t fail tests for missing interpreters: {config,true,false} choice

--workdir <path>

tox working directory