strict-kwargs

Enforce using keyword arguments where possible.

strict-kwargs is a standalone CLI implemented in Rust.

For example, if we have a function which takes two regular arguments, there are three ways to call it. With this tool, only the form where keyword arguments are used is accepted.

"""Showcase errors when calling a function without naming the arguments."""


def add(a: int, b: int) -> int:
    """Add two numbers."""
    return a + b


add(a=1, b=2)  # OK
add(1, 2)  # strict-kwargs reports this; strict-kwargs check --fix can rewrite it
add(1, b=2)  # strict-kwargs reports this; strict-kwargs check --fix can rewrite it

Why?

• Like a formatter, such as black or ruff format, this lets you stop discussing whether a particular function call should use keyword arguments.
• Positional arguments can be fine at first. As more are added, calls can become unclear without anyone stopping to refactor them to keyword arguments.
• Type checkers give better errors when keyword arguments are used. For example, with positional arguments, you may see, Argument 5 to "add" has incompatible type "str"; expected "int". This requires that you count the arguments to see which one is wrong. With named arguments, you get Argument "e" to "add" has incompatible type "str"; expected "int".

Installation

uv tool install strict-kwargs

or:

pip install strict-kwargs

This is tested on Python 3.11+.

Usage

strict-kwargs check .                         # check a directory
strict-kwargs check --output-format json .    # emit check diagnostics as JSON
strict-kwargs check --output-format github .  # emit GitHub Actions annotations
strict-kwargs check --fix .                   # rewrite positional args in place
strict-kwargs check --diff .                  # preview fixes, write nothing
strict-kwargs check --fix --unsafe-fixes .    # include behavior-changing fixes
strict-kwargs check --python .venv .          # point type resolution at an environment
strict-kwargs check --cache-dir .strict-kwargs-cache .  # enable the diagnostic cache

Exit codes are:

• 0: clean
• 1: violations found
• 2: operational error

Output

• full, the default check output, writes Ruff-style diagnostics and summaries to stdout.
• json and github write diagnostics to stdout so machine consumers can read them without mixing in operational messages.
• Warnings and operational errors are always written to stderr.
• check --diff writes the unified diff to stdout and its summary to stderr.

Fix behavior

check --fix only rewrites calls whose target parameter names are known unambiguously. Ambiguous calls are counted as declined.

By default, check --fix rewrites:

• single-signature calls
• overloaded calls, when one precise overload arm can be selected and the rewritten argument types are precise enough

Synthesized constructors are treated as unsafe fixes because generated constructor models can differ from runtime behaviour when class construction is customized.

• --unsafe-fixes: include dataclass and NamedTuple constructor calls whose signatures were synthesized from fields.

Python environment

Use --python to point third-party resolution at an interpreter, virtual environment, or sys.prefix.

• Missing paths are errors.
• A missing --python path is warned about and ignored.

pre-commit

repos:
  - repo: https://github.com/adamtheturtle/strict-kwargs-pre-commit
    rev: 2026.8.28.post2  # pin to a release tag
    hooks:
      - id: strict-kwargs

Configuration

Configuration lives in pyproject.toml:

[tool.strict_kwargs]
required_version = ">=2026.5.19-post.3"
ignore_names = ["main.func", "builtins.str"]
src = ["src"]
namespace_packages = ["src/airflow/providers"]
extend_exclude = ["generated", "vendor"]
force_exclude = true
cache_dir = ".strict-kwargs-cache"
fix_synthesized_constructors = true
error_on_unused_noqa = true
output_format = "full"  # or "json", "github"

Set required_version to make older or incompatible strict-kwargs binaries fail fast when they read this project configuration. Supported specifiers are exact versions, such as 2026.5.19-post.3, and minimum versions, such as >=2026.5.19-post.3. Use the version reported by strict-kwargs --version.

Ignored functions

Use ignore_names for functions that should still allow positional arguments. This is useful especially for builtins which can look strange with keyword arguments.

For example, str(object=1) is not idiomatic.

Suppressing individual findings

Add a Ruff-style # noqa comment to the line a diagnostic is reported on (the first line of the offending call) to suppress it:

func(1, 2, 3)  # noqa: KW001

• # noqa: KW001 suppresses only KW001. A directive naming other codes (for example # noqa: E501) leaves the call reported.
• A bare # noqa suppresses every finding on the line, matching Ruff.
• Suppressed calls are skipped by --fix too, so a # noqa call is never rewritten.

For a call spanning multiple lines, put the comment on the first line, the line the path:line:col output points at:

func(  # noqa: KW001
    1,
    2,
    3,
)

Finding # noqa comments that are no longer needed

Set error_on_unused_noqa = true (or pass --error-on-unused-noqa) to report a KW002 error for every # noqa: KW001 directive that suppressed nothing:

main.py:3:12: KW002 Unused `noqa` directive (unused: `KW001`)

Only directives that name KW001 explicitly are reported. A bare # noqa, or one naming only other tools' codes, is left alone: strict-kwargs sees only its own rule, so it cannot tell whether such a directive is suppressing someone else's finding.

KW002 errors count towards the exit code of check. They belong to checking rather than fixing: --error-on-unused-noqa cannot be combined with --fix or --diff, and those modes neither report nor remove unused directives even when the rule is enabled in pyproject.toml. Enabling the rule makes suppressed calls cost a full check (including the ty fallback), so a run with many # noqa comments is somewhat slower.

Using # noqa alongside Ruff

If you also run Ruff with RUF100 (unused noqa) enabled, prefer the coded form # noqa: KW001: Ruff leaves a directive whose only codes it does not recognise untouched, but it will remove a bare # noqa it considers unused. To keep KW001 from being stripped when it shares a directive with a Ruff code (for example # noqa: E501, KW001), declare it as an external code:

[tool.ruff.lint]
external = ["KW001"]

Source discovery

Set src to source-code directories that should be:

• searched for first-party imports
• stripped when deriving module names

Relative paths are resolved against the project root. For example, src = ["src"] maps src/pkg/mod.py to pkg.mod while preserving the repository root as a fallback source root.

Set namespace_packages to directories that should be treated as namespace packages for module resolution even when they have no __init__.py.

Exclusions

Use extend_exclude to skip generated or vendored Python files during directory runs.

• Patterns use .gitignore-style matching relative to the project root.
• By default, exclusions apply to directory traversal only.
• An explicitly passed file, such as strict-kwargs check generated/api.py, is still checked.
• Set force_exclude = true to apply exclusions to explicitly passed files too. This is useful when pre-commit passes changed files directly.
• The built-in skips for dot-directories, venv, and __pycache__ remain enabled.

Cache

Set cache_dir to enable the persistent diagnostic cache for strict-kwargs checks. Relative cache_dir values in pyproject.toml are resolved against the project root.

The cache location precedence is:

1. --cache-dir
2. [tool.strict_kwargs].cache_dir
3. STRICT_KWARGS_CACHE_DIR

If none are set, the cache is disabled.

Fix defaults

Set fix_synthesized_constructors = true to make strict-kwargs check --fix include dataclass and NamedTuple constructor rewrites without passing --unsafe-fixes each time.

To find the name of a function to ignore, set the following configuration:

[tool.strict_kwargs]
debug = true

Then run strict-kwargs check and look for the debug output.

Comparison with mypy-strict-kwargs

mypy-strict-kwargs is a mypy plugin that enforces the same rule during type checking.

Use strict-kwargs if you:

• type-check with ty
• prefer a standalone linter without plugins
• want automatic rewrites with strict-kwargs check --fix