Setup

Install

uv add --dev "gerenuk[ty]"        # from PyPI (a maturin-built wheel)
uvx --from "gerenuk[ty]" gerenuk impacted-tests   # one-off, no install

From a pip world, pip install "gerenuk[ty]".

What gets installed, and why

gerenuk shells out to tyf (from ty-find), which in turn drives ty’s language server.

ty is an extra rather than a dependency deliberately. It is a pre-1.0 type checker that projects tend to pin for their own use, and a hard requirement in gerenuk would compete with that pin for no benefit: when tyf finds no ty on PATH it falls back to uvx ty. So uv add --dev gerenuk works on its own if uv is around — the first call just pays a download.

Install the extra when you want the version pinned in your lockfile, or when the machine running gerenuk has no network.

changed-symbols needs none of this: it uses git and nothing else.

From source:

git clone https://github.com/mojzis/gerenuk
cd gerenuk
cargo install --path .

Verify

$ gerenuk doctor
workspace: /home/you/proj
tyf:       /home/you/proj/.venv/bin/tyf

If tyf lives somewhere unusual, point GERENUK_TYF at it:

GERENUK_TYF=/opt/bin/tyf gerenuk doctor

Workspace detection

By default gerenuk walks up from the current directory until it finds a pyproject.toml, setup.py, setup.cfg, or .git. Override it with --workspace PATH when you want to run against a project you are not standing in.

Telling coding agents about it

Paste this into your project’s CLAUDE.md. It is deliberately two lines — the exit codes, the run_all verdict and the static-reference caveat are all in gerenuk --help and on this site, and an agent that needs them can read them there:

### `gerenuk` — test selection and dead code

- `gerenuk run -- -q` runs only the tests the working tree's diff impacts
  (`--dry-run` to inspect; `gerenuk impacted-tests` explains why).
- `gerenuk audit <file>` confirms a symbol vulture flagged is really unused;
  its `only tests reach it` findings are ones vulture cannot produce.