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. Note that config-settings options can optionally be prefixed with skbuild., for example -C skbuild.logging.level=INFO.

Verbosity¶

By default, the CMake configuration output is always shown, but it may be hidden behind the build frontend setting, e.g. pip requires including -v argument in order to display any output.

You can increase the verbosity of the build with two settings - build.verbose is a shortcut for verbose build output (i.e. cmake --build ... -v), 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]
build.verbose = true
logging.level = "INFO"

config-settings

$ uv pip install . -v -Cbuild.verbose=true -Clogging.level=INFO

pip

$ pip install . -v -Cbuild.verbose=true -Clogging.level=INFO

build

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

cibuildwheel

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

Environment

SKBUILD_BUILD_VERBOSE: true
SKBUILD_LOGGING_LEVEL: "INFO"

Warning

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

Changed in version 0.10: cmake.verbose was renamed to build.verbose.

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 = "0.12"

In your pyproject.toml, you can specify the special string "build-system.requires", which will read the minimum version from your build-system requirements directly; you must specify a minimum there to use this automatic feature.

[build-system]
requires = ["scikit-build-core>=0.12"]

[tool.scikit-build]
minimum-version = "build-system.requires"

Changed in version 0.10: The "build-system.requires" option was added.

Warning

The following behaviors are affected by minimum-version:

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.
minimum-version 0.10+ (or unset) cmake.targets and cmake.verbose are replaced with build.targets and build.verbose. The CMake minimum version will be detected if not given.
minimum-version 0.12+ (or unset) uses "default" instead of "classic" as the default for sdist.inclusion-mode.
minimum-version 1.0+ (or unset) deprecates the tool.scikit-build.metadata table in favor of the standard top-level [[tool.dynamic-metadata]]; see Dynamic metadata.

Changed in version 0.12.2: Non-normalized SDist names used to be enabled when set to below 0.5. This is no longer supported on PyPI, so this back-compat feature was removed.

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 try to read the version from your CMakeLists.txt with the special string "CMakeLists.txt". This is an error if the minimum version was not statically detectable in the file. If your minimum-version setting is unset or set to “0.10” or higher, scikit-build-core will still try to read this if possible, and will fall back on “>=3.15” if it can’t read it.

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 supported CMake 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"]

You can select a couple of alternative modes, as well. If you want to manually control this, without reading .gitignore, use:

[tool.scikit-build]
sdist.inclusion-mode = "manual"

There’s also a "classic" mode, which fully traverses all directories to check rules (this was the default before scikit-build-core 0.12).

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, where <package_name> is your project’s name. If you want to list packages explicitly, you can. The final path element is the package.

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

Each entry names a single top-level package directory, and the final path element becomes the importable package name. This is not a search directory like setuptools’ tool.setuptools.packages.find.where: subpackages and data files inside a listed package are copied in automatically (recursively), so you never list subpackages. To ship two separate top-level packages, list both:

[tool.scikit-build]
wheel.packages = ["src/pkg_a", "src/pkg_b"]

Auto-detection only looks for a package matching your project name at the three locations above; if you have multiple top-level packages, or your package lives elsewhere, you must list them explicitly.

This can also be a table, allowing full customization of where a source package maps to a wheel directory. The final components of both paths must match due to the way editable installs work. The equivalent of the above is:

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

But you can also do more complex moves:

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

Added in version 0.10: Support for the table form.

You can disable Python file inclusion entirely, and rely only on CMake’s install mechanism:

[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"

You can target a different wheel tree by prefixing the install dir with the matching SKBUILD_*_DIR CMake variable name:

[tool.scikit-build]
wheel.install-dir = "${SKBUILD_DATA_DIR}/mypackage"

The available trees match the SKBUILD_*_DIR cache variables available from within CMake, described in install directories.

Added in version 1.0: Targeting other wheel trees with the ${SKBUILD_<TREE>_DIR} prefix.

Warning

When passing this through PEP 517 config-settings on a command line, quote it so the shell does not expand ${SKBUILD_DATA_DIR} as an environment variable (e.g. -C 'wheel.install-dir=${SKBUILD_DATA_DIR}/mypackage').

The older leading-slash spelling (/data, /scripts, …) selects the same trees but is gated behind experimental = true, and deprecated.

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: Previously 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).

Customizing the output wheel¶

The python API tags for your wheel will be correct assuming you are building a normal CPython extension. For anything else, set wheel.py-api to the tag you support:

[tool.scikit-build]
wheel.py-api = "cp38"

`wheel.py-api`	Use for	Resulting tags
`"cp38"`	Limited API / Stable ABI extension (CPython 3.8+)	`cp38-abi3`
`"py3"`	Extension not using the Python API	`py3-none`
`"py2.py3"`	Same, but installable on Python 2 as well	`py2.py3-none`
`"cp315t"`	Free-threaded stable ABI (PEP 803)	`cp315-abi3t`
`"cp315.cp315t"`	Both stable ABIs from one free-threaded build	`cp315-abi3.abi3t`

Scikit-build-core will only target ABI3 if the version of Python is equal to or newer than the one you set. cp315t also sets Py_TARGET_ABI3T (if using CMake 4.4+). For py3/py2.py3, you still need a version of Python scikit-build-core supports to build the initial wheel. The ${SKBUILD_SABI_COMPONENT} variable and the USE_SABI idiom on the CMake side is covered in Limited API / Stable ABI.

With cp315.cp315t, a free-threaded build emits the combined cp315-abi3.abi3t tag: abi3t is a subset of abi3 (PEP 803), so the single free-threaded binary also loads under a GIL-enabled CPython 3.15+, and the one wheel is installable on every CPython 3.15+. On a GIL build only abi3 can be produced, so it falls back to cp315-abi3.

Added in version 1.0: The free-threaded stable ABI (cp315t, PEP 803) and the combined cp315.cp315t tag.

Some older versions of pip are unable to load standard universal tags; scikit-build-core can expand the macOS universal tags for you for maximum historic compatibility if you’d like:

[tool.scikit-build]
wheel.expand-macos-universal-tags = true

You can also specify a build tag:

pyproject.toml

[tool.scikit-build]
wheel.build-tag = 1

config-settings

$ uv pip install . -Cwheel.build-tag=1

pip

$ pip install . -Cwheel.build-tag=1

build

$ pipx run build --wheel -Cwheel.build-tag=1

cibuildwheel

[tool.cibuildwheel.config-settings]
"wheel.build-tag" = 1

Environment

SKBUILD_WHEEL_BUILD_TAG: "1"

You can select only specific components to install:

[tool.scikit-build]
install.components = ["python"]

And you can turn off binary stripping:

pyproject.toml

[tool.scikit-build]
install.strip = false

config-settings

$ uv pip install . -Cinstall.strip=false

pip

$ pip install . -Cinstall.strip=false

build

$ pipx run build --wheel -Cinstall.strip=false

cibuildwheel

[tool.cibuildwheel.config-settings]
"install.strip" = false

Environment

SKBUILD_INSTALL_STRIP: "false"

You can opt in to reproducible wheels (unlike SDists, this is off by default). When enabled, archive timestamps and file permissions are normalized, and SOURCE_DATE_EPOCH is exported to the CMake build (if not already set) so compilers that honor it can produce deterministic output. This cannot make the compiled binaries themselves reproducible on its own; that also depends on a recent compiler and flags like -ffile-prefix-map.

[tool.scikit-build]
wheel.reproducible = true

Added in version 1.0.

Force-including files¶

Added in version 1.0.

Sometimes you need to place a specific file (or directory) at a specific path in a distribution, even if it lives outside your package tree or is produced elsewhere. Each distribution has its own force-include table mapping source paths to destinations:

[tool.scikit-build.sdist.force-include]
"../shared/data.json" = "mypackage/data.json"

[tool.scikit-build.wheel.force-include]
"vendor/lib.so" = "mypackage/_lib.so"
"tools/run.sh"  = "${SKBUILD_SCRIPTS_DIR}/run.sh"

The keys are source paths relative to the project root; they may point outside it (e.g. ../shared) or be absolute, and ~ is expanded. A source may be a file or a directory, and directories are copied recursively (skipping VCS and __pycache__ junk). A missing source is an error.

sdist.force-include destinations are relative to the SDist root. wheel.force-include destinations are relative to the platlib (the package area), and also accept a ${SKBUILD_<TREE>_DIR} prefix to target a different wheel tree, exactly as with wheel.install-dir above. Force-included wheel files are placed last, so they override discovered package files and CMake output at the same destination.

A force-included file also overrides the matching exclude list (wheel.exclude for wheels, sdist.exclude for SDists): naming an exact source is an explicit request, so it wins even if an exclude pattern matches its destination. A force-included directory stays subject to that exclude, so a bulk tree copy can still be trimmed by an exclude pattern (e.g. force-include a directory and exclude **/*.bzl to drop the Bazel files from it).

In an editable install using redirect mode (the default), platlib entries are served live from their sources through the import redirect instead of being copied, so edits to a force-included file take effect without reinstalling. This covers importable modules (even renamed ones) and data files that keep their filename and sit directly inside a top-level package. Anything the redirect cannot express, like other wheel trees like ${SKBUILD_SCRIPTS_DIR}, renamed or top-level data files, and data files nested below a package subdirectory (kept as real files so package-root resource lookups keep the wheel layout), are still copied at install time, so those snapshots only refresh on reinstall.

Building a wheel from an SDist¶

A common pattern vendors an external (../) source into the SDist and then ships that output in the wheel. Reference the SDist destination as the wheel source and it works in both build modes:

[tool.scikit-build.sdist.force-include]
"../shared/data.json" = "mypackage/data.json"   # vendor it into the SDist

[tool.scikit-build.wheel.force-include]
"mypackage/data.json" = "mypackage/data.json"    # ship the SDist output

When the wheel is built from the unpacked SDist, mypackage/data.json exists and is used directly. When it is built from the source tree (or an editable install) the file was never materialized; a wheel.force-include source missing on disk is then resolved through sdist.force-include (by exact destination, or under a force-included directory) and read from that original source instead. An on-disk file always wins, so the vendored copy is preferred when present.

For cases the automatic resolution cannot express (such as if the wheel source is the original external path rather than the SDist output) use overrides keyed on from-sdist, with a separate wheel.force-include entry gated on each build mode (source tree vs. wheel-from-SDist):

[tool.scikit-build.sdist.force-include]
"../outside.txt" = "vendored/blob.txt"   # vendor it into the SDist

[[tool.scikit-build.overrides]]
if.from-sdist = false                     # source-tree build: read the original
wheel.force-include."../outside.txt" = "mypackage/blob.txt"

[[tool.scikit-build.overrides]]
if.from-sdist = true                      # wheel-from-SDist: read the vendored copy
wheel.force-include."vendored/blob.txt" = "mypackage/blob.txt"

Environment variables for the build¶

Added in version 1.0.

The [tool.scikit-build.env] table sets environment variables for the CMake configure, build, and install subprocesses. Use it for things CMake or the generator read from the environment:CC/CXX, CFLAGS, CMAKE_PREFIX_PATH, compiler launchers, parallel-build level, and so on. For CMake -D cache entries, use cmake.define instead.

Each value is a literal string, or a table that reads from another environment variable ({ env = "OTHER", default = "..." }). By default a variable is only set if it is not already present (setdefault); add force = true to overwrite an existing value. If a value resolves to nothing (its env source is unset and there is no default), the key is skipped. This pairs well with [[tool.scikit-build.overrides]] for platform- or state-specific values.

[tool.scikit-build.env]
SOME_VAR = "some-value"
CMAKE_PREFIX_PATH = { env = "CMAKE_PREFIX_PATH", default = "/opt/mydeps" }

A common use is forwarding a project’s historical parallelism variable (such as MAX_JOBS) to CMAKE_BUILD_PARALLEL_LEVEL:

[tool.scikit-build.env]
CMAKE_BUILD_PARALLEL_LEVEL = { env = "MAX_JOBS" }

A directly-set CMAKE_BUILD_PARALLEL_LEVEL still wins, since env entries use setdefault semantics unless force = true is given.

Note

This table is independent of the if.env override condition. if.env only matches against the ambient process environment and does not see variables you define here.

The table form ({ env = ..., default = ..., force = ... }) is pyproject.toml only; via config-settings or SKBUILD_ENV_* you can only set a literal value.

Selecting a compiler¶

To pick a specific compiler – for example, to use GCC instead of MSVC on a Windows runner – set CC/CXX, optionally scoped to a platform with an override:

[[tool.scikit-build.overrides]]
if.platform-system = "win32"
env.CC = "gcc"
env.CXX = "g++"

These take precedence over the compiler scikit-build-core would otherwise pull from Python’s sysconfig, even without force.

By default, scikit-build-core sets CC/CXX from Python’s sysconfig compiler when they are not already set. If a project’s compiler probes break on that compiler (a conda narrow sysroot, a stale venv gcc, a cross or oneAPI toolchain), list the variable in the env table to suppress that default and let CMake detect the compiler from PATH; an entry that reads from the same name does this without pinning a value:

[tool.scikit-build.env]
CC = { env = "CC" }
CXX = { env = "CXX" }

Search paths for dependencies¶

To point CMake at extra prefixes (vcpkg, Homebrew, a custom install tree) when locating dependencies, set CMAKE_PREFIX_PATH:

[tool.scikit-build.env]
CMAKE_PREFIX_PATH = "/opt/mydeps;/usr/local"

For dependencies installed as Python packages in the same environment, the search paths are populated automatically through entry-points; see search paths.

Editable installs¶

Editable installs (pip install -e .) are supported, including an optional (experimental) rebuild-on-import mode and an inplace mode; see the dedicated editable installs page.

Messages¶

You can add a message to be printed after a successful or failed build. For example:

[tool.scikit-build]
messages.after-success = "{green}Wheel successfully built"
messages.after-failure = """
{bold.red}Sorry{normal}, build failed. Your platform is {platform.platform}.
"""

This will be run through Python’s formatter, so escape curly brackets if you need them. Currently, there are several formatter-style keywords available: sys, platform (parenthesis will be added for items like platform.platform for you), __version__ for scikit-build-core’s version, and style keywords.

The style keywords are the standard ANSI colors (red, green, blue, …) and styles (normal, bold, italic, underline, reverse), chainable with dots: bold.red.bg.blue is valid (fg./bg. select foreground/background, foreground being the default, and reset clears all styles). Remember that you need to set the environment variable FORCE_COLOR to see colors with pip.

Added in version 0.10.

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

$ uv pip install . -Cbuild-dir="build/{wheel_tag}"

pip

$ pip install . -Cbuild-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. See Formattable fields. For example, {name} lets a single build-dir shared by every member of a uv or hatch workspace (e.g. via SKBUILD_BUILD_DIR) avoid collisions: SKBUILD_BUILD_DIR=/path/to/cache/{name}/{cache_tag}.

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

The following features currently require this flag:

Wheel variants: PEP 817 variant support (variant, variant-name, variant-label, and null-variant), added in 1.0. See Building wheel variants.
Legacy tool.scikit-build.metadata plugins: dynamic metadata providers not shipped with scikit-build-core (anything using provider-path or a provider outside the scikit_build_core.* namespace) used through the deprecated tool.scikit-build.metadata table. The standard [[tool.dynamic-metadata]] interface supports the same providers without this flag. See Dynamic metadata.
Leading-slash wheel trees: the deprecated absolute spelling (/platlib, /data, /headers, /scripts, /metadata) for wheel.install-dir and wheel.force-include, placed one level above the platlib root. The ${SKBUILD_<TREE>_DIR} prefix is the non-experimental replacement. See wheel.install-dir.

The rebuild-on-import feature for editable installs is also considered experimental and subject to change, but is not gated behind this flag.

You can also fail the build with fail = true. This is useful with overrides if you want to make a specific configuration fail. If this is set, extra dependencies like "cmake" will not be requested.

Added in version 0.10.

Configuration¶

Verbosity¶

Minimum version & defaults¶

CMake and Ninja minimum versions¶

Configuring source file inclusion¶

Customizing the built wheel¶

Customizing the output wheel¶

Force-including files¶

Building a wheel from an SDist¶

Configuring CMake arguments and defines¶

Environment variables for the build¶

Selecting a compiler¶

Search paths for dependencies¶

Editable installs¶

Messages¶

Other options¶

See also¶