Compare lint and format results for two different ruff versions (e.g. main and a PR) on real world projects.

From the Ruff project root, install with uv:

uv tool install -e ./python/ruff-ecosystem

ruff-ecosystem <check | format> <baseline executable> <comparison executable>

Note executable paths may be absolute, relative to the current working directory, or will be looked up in the current Python environment and PATH.

Run ruff check ecosystem checks comparing your debug build to your system Ruff:

ruff-ecosystem check ruff "./target/debug/ruff"

Run ruff format ecosystem checks comparing your debug build to your system Ruff:

ruff-ecosystem format ruff "./target/debug/ruff"

Run ruff format ecosystem checks comparing with changes to code that is already formatted:

ruff-ecosystem format ruff "./target/debug/ruff" --format-comparison ruff-then-ruff

Run ruff format ecosystem checks comparing with the Black formatter:

ruff-ecosystem format black ruff -v --cache python/checkouts --format-comparison black-and-ruff

The default output format is markdown, which includes nice summaries of the changes. You can use --output-format json to display the raw data — this is particularly useful when making changes to the ecosystem checks.

When developing, it can be useful to set the --pdb flag to drop into a debugger on failure:

ruff-ecosystem check ruff "./target/debug/ruff" --pdb

You can also provide a path to cache checkouts to speed up repeated runs:

ruff-ecosystem check ruff "./target/debug/ruff" --cache ./repos