Formatting Style Guide

Settings live in pyproject.toml; the hooks that apply them live in .pre-commit-config.yaml. Both are the source of truth — this file summarizes them.

2-space indentation, never tabs (pyink-indentation = 2).
80-character lines (pyink line-length = 80). Import lines are the exception — see the imports reference.
pyink (Google's Black fork) formats Python.
Quotes follow whichever style already dominates the file (pyink-use-majority-quotes), so pyink will not rewrite 'x' to "x". Match the file you are editing instead of churning quotes.
isort sorts imports with profile = "google".

What each hook enforces

Run order matters less than knowing which tool rejected the commit.

Hook	What it does
`ruff`	Removes unused imports only (`lint.select = ["F401"]`), auto-fixed, `src/` only. `__init__.py` is exempt because its imports are re-exports.
`isort`	Import order and grouping.
`pyink`	All other formatting.
`addlicense`	Adds the Apache 2.0 header to `.py`/`.sh`. Skipped with a warning if the Go binary is not installed; CI still catches it.
`check-new-py-prefix`	New files under `src/google/adk/` need a `_` prefix — see the visibility reference.
`compliance-checks`	Logger name, `from __future__ import annotations`, `cli/` import direction, mTLS endpoints.
`codespell`	Spelling in code and prose. Add a genuine false positive to `ignore-words-list` in `pyproject.toml`.
`pyproject-fmt`	Normalizes `pyproject.toml` itself.
`mdformat`	`README.md`, `CONTRIBUTING.md`, and `contributing/**.md` only.
`check-yaml`, `end-of-file-fixer`, `trailing-whitespace`	Whitespace and YAML syntax hygiene.
`update-constraints`	Regenerates `constraints-3.*.txt` when `pyproject.toml` changes. Needs network access.

src/google/adk/cli/browser/, src/google/adk/v1/, and v1_tests/ are excluded from every hook.

Running the formatter

Install the git hook once so formatting happens on commit:

bash

pre-commit install

Then, to check work that is not yet committed:

bash

# Staged files only (this is what the commit hook runs)
pre-commit run

# Specific files
pre-commit run --files {path/to/file.py}

# Everything
pre-commit run --all-files

CI runs this same config, so a clean pre-commit run --all-files means the lint job will pass. Type errors are a separate CI job — see the typing reference.

Use the adk-setup skill to install pre-commit, addlicense, and the rest of the toolchain.