Antigravity rules

What a rules pack is

A rules pack is a markdown document an Antigravity agent loads at startup — rules/*.md in the official customization scheme. It is not configuration in the usual sense: nothing is compiled, nothing is validated, and no error is raised when a rule is malformed. It is standing instruction the model reads before it acts, which means a good pack is short, specific and written in the imperative — cap the diff, refuse out-of-scope writes, ask before touching tests.

Because the agent follows rules only as far as its context allows, length is the enemy. A two-page pack of precise constraints outperforms a twenty-page manifesto of good intentions; the model weighs every line, and vague lines dilute the ones that matter. The packs on this page are grouped by the problem they solve rather than by author — single-purpose guards that do one thing well alongside opinionated baselines a team adopts on day one.

How to evaluate a pack before you install it

Read it the way the agent will: top to bottom, no skipping. If a rule is vague — "write clean code", "follow best practices" — it will not change behavior. Every rule should be checkable against a diff.
Check what it does on conflict. A pack that quietly widens its own scope when the agent is unsure is worse than no pack. The good ones say what to do when rules collide.
Look at the repository it came from. A pack tuned for a monorepo behaves differently inside a single package, and one written for a greenfield project can strangle a legacy codebase.
Check the maintenance signal. Rules interact with a fast-moving product — a pack untouched for six months may constrain behavior that no longer exists.

Official versus third-party packs

Google ships starter rules inside the product and documents the format at antigravity.google, but the ecosystem of shared packs is community-built — repositories, gists and team-internal baselines published for reuse. Verification here means reading the pack against its repository and, where the pack is installable, loading it on a real project to see what it does to a live diff.

Rules sit at the base of the Antigravity customization stack — skills assume them, agents inherit them, and a bad rule undermines everything layered on top. That is why this page leads with the smallest packs: start with a guard that solves one problem you actually have, and add rules when a real review caught something, not speculatively.