Configuration¶

Scikit-build-core supports a powerful unified configuration system. Every option in scikit-build-core can be specified in one of three ways: as a pyproject.toml option (preferred if static), as a config-settings options (preferred if dynamic), or as an environment variable.

Verbosity¶

You can increase the verbosity of the build with two settings - cmake.verbose is a shortcut for verbose build output, and logging.level controls scikit-build-core’s internal logging. An example (with all configuration styles) of setting both is:

pyproject.toml

[tool.scikit-build]
cmake.verbose = true
logging.level = "INFO"

config-settings

pip

$ pip install . -v --config-settings=cmake.verbose=true --config-settings=logging.level=INFO

build

$ pipx run build --wheel -Ccmake.verbose=true -Clogging.level=INFO

cibuildwheel

[tool.cibuildwheel.config-settings]
"cmake.verbose" = true
"logging.level" = "INFO"

Environment

SKBUILD_CMAKE_VERBOSE: true
SKBUILD_LOGGING_LEVEL: "INFO"

Note

When using pip, make sure you include at least a -v argument so that the verbosity settings above are displayed.

Warning

In general, the environment variable method is intended as an emergency workaround for legacy tooling.

Minimum version & defaults¶

Scikit-build-core, like CMake, has a special minimum required version setting. If you set this, you get two benefits. First, if the version is less than this version, you get a nice error message. But, more importantly, if scikit-build-core is a newer version than the version set here, it will select older defaults to help ensure your package can continue to build, even if a default value changes in the future. This should help reduce the chance of ever needed an upper cap on the scikit-build-core version, as upper caps are discouraged.

It is recommended you set this value as high as you feel comfortable with, and probably keep in sync with your build-system requirements.

[tool.scikit-build]
minimum-version = "0.2"

Warning

The following behaviors are affected by minimum-version:

minimum-version 0.5+ (or unset) provides the original name in metadata and properly normalized SDist names.
minimum-version 0.5+ (or unset) strips binaries by default.
minimum-version 0.8+ (or unset) cmake.minimum-version and ninja.minimum-version are replaced with cmake.version and ninja.version.

CMake and Ninja minimum versions¶

You can select a different minimum version for CMake and Ninja. Scikit-build-core will automatically decide to download a wheel for these (if possible) when the system version is less than this value.

For example, to require a recent CMake and Ninja:

[tool.scikit-build]
cmake.version = ">=3.26.1"
ninja.version = ">=1.11"

You can also enforce ninja to be required even if make is present on Unix:

[tool.scikit-build]
ninja.make-fallback = false

You can also control the FindPython backport; by default, a backport of CMake 3.26.1’s FindPython will be used if the CMake version is less than 3.26.1; you can turn this down if you’d like (“3.15”, scikit-build-core’s minimum version, would turn it off).

[tool.scikit-build]
backport.find-python = "3.15"

Added in version 0.8: These used to be called cmake.minimum-version and ninja.minimum-version, and only took a single value. Now they are full specifier sets, allowing for more complex version requirements, like >=3.15,!=3.18.0.

Configuring source file inclusion¶

Scikit-build-core defaults to using your .gitignore to select what to exclude from the source distribution. You can list files to explicitly include and exclude if you want:

[tool.scikit-build]
sdist.include = ["src/some_generated_file.txt"]
sdist.exclude = [".github"]

By default, scikit-build-core will respect SOURCE_DATE_EPOCH, and will lock the modification time to a reproducible value if it’s not set. You can disable reproducible builds if you prefer, however:

[tool.scikit-build]
sdist.reproducible = false

You can also request CMake to run during this step:

[tool.scikit-build]
sdist.cmake = true

Note

If you do this, you’ll want to have some artifact from the configure in your source directory; for example:

include(FetchContent)

set(PYBIND11_FINDPYTHON ON)

if(NOT SKBUILD_STATE STREQUAL "sdist"
   AND EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/pybind11/CMakeLists.txt")
  message(STATUS "Using integrated pybind11")
  add_subdirectory(pybind11)
else()
  FetchContent_Declare(
    pybind11
    GIT_REPOSITORY https://github.com/pybind/pybind11.git
    GIT_TAG v2.12.0
    SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/pybind11)
  FetchContent_MakeAvailable(pybind11)
endif()

The /pybind11 directory is in the .gitignore and important parts are in sdist.include:

[tool.scikit-build]
sdist.cmake = true
sdist.include = [
  "pybind11/tools",
  "pybind11/include",
  "pybind11/CMakeLists.txt",
]

Customizing the built wheel¶

The wheel will automatically look for Python packages at src/<package_name>, python/<package_name>, and <package_name>, in that order. If you want to list packages explicitly, you can. The final path element is the package.

[tool.scikit-build]
wheel.packages = ["python/src/mypackage"]

Or you can disable Python file inclusion entirely, and rely only on CMake’s install mechanism, you can do that instead:

[tool.scikit-build]
wheel.packages = []

The install directory is normally site-packages; however, you can manually set that to a different directory if you’d like to avoid changing your CMake files. For example, to mimic scikit-build classic:

[tool.scikit-build]
wheel.install-dir = "mypackage"

Warning

You can select a different wheel target directory, as well, but that syntax is experimental; install to ${SKBUILD_DATA_DIR}, etc. from within CMake instead for now.

By default, any LICEN[CS]E*, COPYING*, NOTICE*, or AUTHORS* file in the root of the build directory will be picked up. You can specify an exact list of files if you prefer, or if your license file is in a different directory. Globbing patterns are supported.

[tool.scikit-build]
wheel.license-files = ["LICENSE"]

You can exclude files from the built wheel (on top of the sdist.exclude list) as well (not guaranteed to be respected by editable installs):

[tool.scikit-build]
wheel.exclude = ["**.pyx"]

Changed in version 0.9: Before scikit-build-core 0.9, these were matched on the source path, rather than the wheel path, and didn’t apply to CMake output.

Note

There are two more settings that are primarily intended for overrides (see below). wheel.cmake defaults to true, and this enables/disables building with CMake. It also changes the default of wheel.platlib unless it’s set explicitly; CMake builds assume wheel.platlib = true, and CMake-less builds assume wheel.platlib = false (purelib targeted instead).

Dynamic metadata¶

Scikit-build-core 0.3.0+ supports dynamic metadata with two built-in plugins.

Warning

This is not ready for plugin development outside of scikit-build-core; tool.scikit-build.experimental=true is required to use plugins that are not shipped with scikit-build-core, since the interface is provisional and may change between minor versions.

Setuptools-scm

You can use setuptools-scm to pull the version from VCS:

[project]
name = "mypackage"
dynamic = ["version"]

[tool.scikit-build]
metadata.version.provider = "scikit_build_core.metadata.setuptools_scm"
sdist.include = ["src/package/_version.py"]

[tool.setuptools_scm]  # Section required
write_to = "src/package/_version.py"

This sets the python project version according to git tags or a .git_archival.txt file, or equivalents for other VCS systems.

If you need to set the CMake project version without scikit-build-core (which provides ${SKBUILD_PROJECT_VERSION}), you can use something like DynamicVersion module from github.com/LecrisUT/CMakeExtraUtils:

# Import `CMakeExtraUtils` or bundle `DynamicVersion.cmake` from there
include(DynamicVersion)

# Set ${PROJECT_VERSION} according to git tag or `.git_archival.txt`
dynamic_version()

project(MyPackage VERSION ${PROJECT_VERSION})

Fancy-pypi-readme

You can use hatch-fancy-pypi-readme to render your README:

[project]
name = "mypackage"
dynamic = ["readme"]

[tool.scikit-build]
metadata.readme.provider = "scikit_build_core.metadata.fancy_pypi_readme"

# tool.hatch.metadata.hooks.fancy-pypi-readme options here

Regex

If you want to pull a string-valued expression (usually version) from an existing file, you can the integrated regex plugin to pull the information.

name = "mypackage"
dynamic = ["version"]

[tool.scikit-build.metadata.version]
provider = "scikit_build_core.metadata.regex"
input = "src/mypackage/__init__.py"

You can set a custom regex with regex=; use (?P<value>...) to capture the value you want to use. By default when targeting version, you get a reasonable regex for python files, '(?i)^(__version__|VERSION) *= *([\'"])v?(?P<value>.+?)\2'.

Added in version 0.5.

Writing metadata¶

You can write out metadata to file(s) as well. Other info might become available here in the future, but currently it supports anything available as strings in metadata. (Note that arrays like this are only supported in TOML configuration.)

[[tool.scikit-build.generate]]
path = "package/_version.py"
template = '''
version = "${version}"
'''

template or template-path is required; this uses string.Template formatting. There are three options for output location; location = "install" (the default) will go to the wheel, location = "build" will go to the CMake build directory, and location = "source" will write out to the source directory (be sure to .gitignore this file. It will automatically be added to your SDist includes. It will overwrite existing files).

The path is generally relative to the base of the wheel / build dir / source dir, depending on which location you pick.

Editable installs¶

Experimental support for editable installs is provided, with some caveats and configuration. Recommendations:

Use --no-build-isolation when doing an editable install is recommended; you should preinstall your dependencies.
Automatic rebuilds do not have the original isolated build dir (pip deletes it), so select a build-dir when using editable installs, especially if you also enable automatic rebuilds.
You need to reinstall to pick up new files.

Known limitations:

Resources (via importlib.resources) are not properly supported (yet). Currently experimentally supported except on Python 3.9 (3.7, 3.8, 3.10, 3.11, and 3.12 work). importlib_resources may work on Python 3.9.

# Very experimental rebuild on initial import feature
$ pip install --no-build-isolation --config-settings=editable.rebuild=true -Cbuild-dir=build -ve.

Due to the length of this line already being long, you do not need to set the experimental setting to use editable installs, but please consider them experimental and subject to change.

You can disable the verbose rebuild output with editable.verbose=false if you want. (Also available as the SKBUILD_EDITABLE_VERBOSE envvar when importing; this will override if non-empty, and "0" will disable verbose output).

The default editable.mode, "redirect", uses a custom redirecting finder to combine the static CMake install dir with the original source code. Python code added via scikit-build-core’s package discovery will be found in the original location, so changes there are picked up on import, regardless of the editable.rebuild setting.

Note

A second experimental mode, "inplace", is also available. This does an in-place CMake build, so all the caveats there apply too – only one build per source directory, you can’t change to an out-of-source builds without removing the build artifacts, your source directory will be littered with build artifacts, etc. Also, to make your binaries importable, you should set LIBRARY_OUTPUT_DIRECTORY (include a generator expression, like the empty one $<0:> for multi-config generator support, like MSVC, so you don’t have to set all possible *_<CONFIG> variations) to make sure they are placed inside your source directory inside the Python packages; this will be run from the build directory, rather than installed. This will also not support automatic rebuilds. The build directory setting will be ignored if you use this and perform an editable install. You can detect this mode by checking for an in-place build and checking SKBUILD being set.

With all the caveats, this is very logically simple (one directory) and a near identical replacement for python setup.py build_ext --inplace. Some third party tooling might work better with this mode. Scikit-build-core will simply install a .pth file that points at your source package(s) and do an inplace CMake build.

On the command line, you can pass -Ceditable.mode=inplace to enable this mode.

Other options¶

You can select a custom build dir; by default scikit-build-core will use a temporary dir. If you select a persistent one, you can get major rebuild speedups.

pyproject.toml

[tool.scikit-build]
build-dir = "build/{wheel_tag}"

config-settings

pip

$ pip install . --config-settings=build-dir="build/{wheel_tag}"

build

$ pipx run build --wheel -Cbuild-dir="build/{wheel_tag}"

cibuildwheel

[tool.cibuildwheel.config-settings]
"build-dir" = "build/{wheel_tag}"

Environment

SKBUILD_BUILD_DIR: "build/{wheel_tag}"

There are several values you can access through Python’s formatting syntax:

cache_tag: sys.implementation.cache_tag
wheel_tag: The tags as computed for the wheel
build_type: The current build type (Release by default)
state: The current run state, sdist, wheel, editable, metadata_wheel, and metadata_editable

Scikit-build-core also strictly validates configuration; if you need to disable this, you can:

[tool.scikit-build]
strict-config = false

Scikit-build-core also occasionally has experimental features. This is applied to features that do not yet carry the same forward compatibility (using minimum-version) guarantee that other scikit-build-core features have. These can only be used if you enable them:

[tool.scikit-build]
experimental = true

Overrides¶

Scikit-build-core has an override system, similar to cibuildwheel and mypy. You specify a tool.scikit-build.overrides array with an if key. That if key can take several values, including several based on PEP 508:

python-version: The two-digit Python version. Takes a specifier set.
platform-system: The value of sys.platform. Takes a regex.
platform-machine: The value of platform.machine(). Takes a regex.
platform-node: The value of platform.node(). Takes a regex.
implementation-name: The value of sys.implementation.name. Takes a regex.
implementation-version: Derived from sys.implementation.version, following PEP 508. Takes a specifier set.
env: A table of environment variables mapped to either string regexs, or booleans. Valid “truthy” environment variables are case insensitive true, on, yes, y, t, or a number more than 0.
state: The state of the build, one of sdist, wheel, editable, metadata_wheel, and metadata_editable. Takes a regex.

At least one must be provided. Then you can specify any collection of valid options, and those will override if all the items in the if are true. They will match top to bottom, overriding previous matches. For example:

[[tool.scikit-build.overrides]]
if.sys-platform = "darwin"
cmake.version = ">=3.18"

If you use if.any instead of if, then the override is true if any one of the items in it are true.

Full schema¶

The full schema for the tool.scikit-build table is below:

https://github.com/scikit-build/scikit-build-core/blob/main/src/scikit_build_core/resources/scikit-build.schema.json
Scikit-build-core’s settings.
type	object
properties
cmake	type	object
	properties
	minimum-version	DEPRECATED in 0.8; use version instead.
		type	string
	version	The versions of CMake to allow. If CMake is not present on the system or does not pass this specifier, it will be downloaded via PyPI if possible. An empty string will disable this check.
		type	string
		default	=3.15
	args	A list of args to pass to CMake when configuring the project. Setting this in config or envvar will override toml. See also `cmake.define`.
		type	array
		items	type	string
	define	A table of defines to pass to CMake when configuring the project. Additive.
		type	object
		patternProperties
		.+	oneOf	oneOf	type	string
					type	boolean
				type	object
				properties
				env	type	string
					minLength	1
				default	oneOf	type	string
						type	boolean
				additionalProperties	False
	verbose	Verbose printout when building.
		type	boolean
		default	False
	build-type	The build type to use when building the project. Valid options are: “Debug”, “Release”, “RelWithDebInfo”, “MinSizeRel”, “”, etc.
		type	string
		default	Release
	source-dir	The source directory to use when building the project. Currently only affects the native builder (not the setuptools plugin).
		type	string
		default	.
	targets	The build targets to use when building the project. Empty builds the default target.
		type	array
		items	type	string
	additionalProperties	False
ninja	type	object
	properties
	minimum-version	DEPRECATED in 0.8; use version instead.
		type	string
	version	The versions of Ninja to allow. If Ninja is not present on the system or does not pass this specifier, it will be downloaded via PyPI if possible. An empty string will disable this check.
		type	string
		default	=1.5
	make-fallback	If Ninja is not present on the system or is older than required, it will be downloaded via PyPI if this is false.
		type	boolean
		default	True
	additionalProperties	False
logging	type	object
	properties
	level	The logging level to display, “DEBUG”, “INFO”, “WARNING”, and “ERROR” are possible options.
		enum	NOTSET, DEBUG, INFO, WARNING, ERROR, CRITICAL
		default	WARNING
	additionalProperties	False
sdist	type	object
	properties
	include	Files to include in the SDist even if they are skipped by default. Supports gitignore syntax.
		type	array
		items	type	string
	exclude	Files to exclude from the SDist even if they are included by default. Supports gitignore syntax.
		type	array
		items	type	string
	reproducible	If set to True, try to build a reproducible distribution (Unix and Python 3.9+ recommended). `SOURCE_DATE_EPOCH` will be used for timestamps, or a fixed value if not set.
		type	boolean
		default	True
	cmake	If set to True, CMake will be run before building the SDist.
		type	boolean
		default	False
	additionalProperties	False
wheel	type	object
	properties
	packages	A list of packages to auto-copy into the wheel. If this is not set, it will default to the first of `src/<package>`, `python/<package>`, or `<package>` if they exist. The prefix(s) will be stripped from the package name inside the wheel.
		type	array
		items	type	string
	py-api	The Python tags. The default (empty string) will use the default Python version. You can also set this to “cp37” to enable the CPython 3.7+ Stable ABI / Limited API (only on CPython and if the version is sufficient, otherwise this has no effect). Or you can set it to “py3” or “py2.py3” to ignore Python ABI compatibility. The ABI tag is inferred from this tag.
		type	string
		default
	expand-macos-universal-tags	Fill out extra tags that are not required. This adds “x86_64” and “arm64” to the list of platforms when “universal2” is used, which helps older Pip’s (before 21.0.1) find the correct wheel.
		type	boolean
		default	False
	install-dir	The install directory for the wheel. This is relative to the platlib root. You might set this to the package name. The original dir is still at SKBUILD_PLATLIB_DIR (also SKBUILD_DATA_DIR, etc. are available). EXPERIMENTAL: An absolute path will be one level higher than the platlib root, giving access to “/platlib”, “/data”, “/headers”, and “/scripts”.
		type	string
		default
	license-files	A list of license files to include in the wheel. Supports glob patterns.
		type	array
		items	type	string
	cmake	If set to True (the default), CMake will be run before building the wheel.
		type	boolean
		default	True
	platlib	Target the platlib or the purelib. If not set, the default is to target the platlib if wheel.cmake is true, and the purelib otherwise.
		type	boolean
	exclude	A set of patterns to exclude from the wheel. This is additive to the SDist exclude patterns. This applies to the final paths in the wheel, and can exclude files from CMake output as well. Editable installs may not respect this exclusion.
		type	array
		items	type	string
	build-tag	The build tag to use for the wheel. If empty, no build tag is used.
		type	string
		default
	additionalProperties	False
backport	type	object
	properties
	find-python	If CMake is less than this value, backport a copy of FindPython. Set to 0 disable this, or the empty string.
		type	string
		default	3.26.1
	additionalProperties	False
editable	type	object
	properties
	mode	Select the editable mode to use. Can be “redirect” (default) or “inplace”.
		enum	redirect, inplace
		default	redirect
	verbose	Turn on verbose output for the editable mode rebuilds.
		type	boolean
		default	True
	rebuild	Rebuild the project when the package is imported. The build-directory must be set.
		type	boolean
		default	False
	additionalProperties	False
install	type	object
	properties
	components	The components to install. If empty, all default components are installed.
		type	array
		items	type	string
	strip	Whether to strip the binaries. True for scikit-build-core 0.5+.
		type	boolean
	additionalProperties	False
generate	type	array
	items	oneOf	type	object
			properties
			path	The path (relative to platlib) for the file to generate.
				type	string
				minLength	1
			template	The template to use for the file. This includes string.Template style placeholders for all the metadata. If empty, a template-path must be set.
				type	string
				minLength	1
			location	The place to put the generated file. The “build” directory is useful for CMake files, and the “install” directory is useful for Python files, usually. You can also write directly to the “source” directory, will overwrite existing files & remember to gitignore the file.
				enum	install, build, source
				default	install
			additionalProperties	False
			type	object
			properties
			path	The path (relative to platlib) for the file to generate.
				type	string
				minLength	1
			template-path	The path to the template file. If empty, a template must be set.
				type	string
				minLength	1
			location	The place to put the generated file. The “build” directory is useful for CMake files, and the “install” directory is useful for Python files, usually. You can also write directly to the “source” directory, will overwrite existing files & remember to gitignore the file.
				enum	install, build, source
				default	install
			additionalProperties	False
metadata	List dynamic metadata fields and hook locations in this table.
	type	object
	properties
	version	:ref:`#/$defs/metadata`
	description	:ref:`#/$defs/metadata`
	license	:ref:`#/$defs/metadata`
	readme	:ref:`#/$defs/metadata`
	requires-python	:ref:`#/$defs/metadata`
	dependencies	:ref:`#/$defs/metadata`
	optional-dependencies	:ref:`#/$defs/metadata`
	entrypoints	:ref:`#/$defs/metadata`
	authors	:ref:`#/$defs/metadata`
	maintainers	:ref:`#/$defs/metadata`
	urls	:ref:`#/$defs/metadata`
	classifiers	:ref:`#/$defs/metadata`
	keywords	:ref:`#/$defs/metadata`
	scripts	:ref:`#/$defs/metadata`
	gui-scripts	:ref:`#/$defs/metadata`
	additionalProperties	False
strict-config	Strictly check all config options. If False, warnings will be printed for unknown options. If True, an error will be raised.
	type	boolean
	default	True
experimental	Enable early previews of features not finalized yet.
	type	boolean
	default	False
minimum-version	If set, this will provide a method for backward compatibility.
	type	string
build-dir	The build directory. Defaults to a temporary directory, but can be set.
	type	string
	default
overrides	A list of overrides to apply to the settings, based on the `if` selector.
	type	array
	items	type	object
		properties
		if	anyOf	:ref:`#/$defs/if_overrides`
				type	object
				properties
				any	:ref:`#/$defs/if_overrides`
				additionalProperties	False
		inherit	type	object
			properties
			cmake	type	object
				properties
				args	:ref:`#/$defs/inherit`
				define	:ref:`#/$defs/inherit`
				targets	:ref:`#/$defs/inherit`
				additionalProperties	False
			sdist	type	object
				properties
				include	:ref:`#/$defs/inherit`
				exclude	:ref:`#/$defs/inherit`
				additionalProperties	False
			wheel	type	object
				properties
				packages	:ref:`#/$defs/inherit`
				license-files	:ref:`#/$defs/inherit`
				exclude	:ref:`#/$defs/inherit`
				additionalProperties	False
			install	type	object
				properties
				components	:ref:`#/$defs/inherit`
				additionalProperties	False
			additionalProperties	False
		cmake	:ref:`#/properties/cmake`
		ninja	:ref:`#/properties/ninja`
		logging	:ref:`#/properties/logging`
		sdist	:ref:`#/properties/sdist`
		wheel	:ref:`#/properties/wheel`
		backport	:ref:`#/properties/backport`
		editable	:ref:`#/properties/editable`
		install	:ref:`#/properties/install`
		generate	:ref:`#/properties/generate`
		metadata	:ref:`#/properties/metadata`
		strict-config	:ref:`#/properties/strict-config`
		experimental	:ref:`#/properties/experimental`
		minimum-version	:ref:`#/properties/minimum-version`
		build-dir	:ref:`#/properties/build-dir`
		additionalProperties	False
		minProperties	2
additionalProperties	False
$defs
metadata	type	object
	properties
	provider	type	string
	provider-path	type	string
if_overrides	type	object
	properties
	python-version	The two-digit Python version. Takes a specifier set.
		type	string
	implementation-name	The value of `sys.implementation.name`. Takes a regex
		type	string
	implementation-version	Derived from `sys.implementation.version`, following PEP 508. Takes a specifier set.
		type	string
	platform-system	The value of `sys.platform`. Takes a regex.
		type	string
	platform-machine	The value of `platform.machine()`. Takes a regex.
		type	string
	platform-node	The value of `platform.node()`. Takes a regex.
		type	string
	state	The state of the build, one of `sdist`, `wheel`, `editable`, `metadata_wheel`, and `metadata_editable`. Takes a regex.
		type	string
	env	A table of environment variables mapped to either string regexs, or booleans. Valid ‘truthy’ environment variables are case insensitive `true`, `on`, `yes`, `y`, `t`, or a number more than 0.
		type	object
		patternProperties
		.*	oneOf	type	string
				type	boolean
		additionalProperties	False
		minProperties	1
	additionalProperties	False
	minProperties	1
inherit	enum	none, append, prepend
	default	none

Configuration¶

Verbosity¶

Minimum version & defaults¶

CMake and Ninja minimum versions¶

Configuring source file inclusion¶

Customizing the built wheel¶

Customizing the output wheel¶

Configuring CMake arguments and defines¶

Dynamic metadata¶

Writing metadata¶

Editable installs¶

Other options¶

Overrides¶

Full schema¶