How to ignore a Ruff rule for a directory

When Ruff flags assert statements in tests, use per-file-ignores to allow them in the test directory while keeping the rule active in application code. For an isolated exception, use a one-line suppression or block suppression instead.

Prerequisites

Use an existing project with Ruff installed, as in the Ruff setup tutorial. Run commands from the project root; the examples assume it contains tests/ and src/ directories.

Add a path-specific exception

In the project’s pyproject.toml, add the following entries, merging into any existing tables:

[tool.ruff.lint]
extend-select = ["S101"]  # Check assert statements throughout the project.

[tool.ruff.lint.per-file-ignores]
"tests/**" = ["S101"]  # Allow assert statements in tests and their subdirectories.

Keep any existing extend-select entries. The exception suppresses S101 only for matching paths; other enabled rules still apply there.

Choose additional patterns only where the project needs them:

Patterns containing a directory are relative to the discovered configuration file’s directory. ** includes nested directories; use "**/tests/**" to match test directories anywhere in the project. Use forward slashes in TOML on Windows too.

Preserve exceptions from inherited configuration

If the project already inherits a configuration with extend, use extend-per-file-ignores instead of the earlier per-file-ignores table to keep inherited exceptions. For example, with an existing ruff-base.toml beside pyproject.toml:

[tool.ruff]
extend = "ruff-base.toml"

[tool.ruff.lint.extend-per-file-ignores]
"tests/**" = ["S101"]

per-file-ignores replaces the inherited per-file-ignores mapping; extend-per-file-ignores adds to it. A nested configuration does not automatically inherit its parent: keep its explicit extend setting.

Check that the exception matched

Re-run the enabled rule against both directories:

uv run ruff check --select S101 tests src

uv run executes the command inside the project’s virtual environment, ensuring all dependencies are installed first.

Assertions under tests/ produce no S101 diagnostics; assertions under src/ still do. If there are no assertions in src/, expect All checks passed!.

If a file still reports the ignored rule, substitute its actual path in this command:

uv run ruff check --show-settings tests/test_example.py

The output identifies the resolved settings file and lists linter.per_file_ignores. Check that Ruff loaded the intended configuration and that its resolved patterns cover the file. Then run the full check without --select to confirm other rules remain enforced:

uv run ruff check .

Expect any remaining diagnostics, including S101 in application code, or All checks passed! if the project is clean.