# CLAUDE.md - this project

Project instructions for Claude Code.

## Project

A Chrome Extension (MV3) + Tailwind CSS v4 + Zustand + Vitest project.

Stack: Chrome Extension (MV3), Tailwind CSS v4, Zustand, Vitest.

## Commands

- Build: `npm run build`
- Dev/watch: `npm run dev`
- Unit tests: `npx vitest run`

## Project structure

- `src/background/` service worker, `src/content/` content scripts, `src/popup/` and `src/options/` UI.

## How to work in this repo

- Read the relevant files before editing. Follow the patterns already in the codebase over these generic rules.
- Make the smallest change that solves the task. Do not refactor or reformat unrelated code.
- Before saying a task is done, run the type-check, lint and tests listed under Commands and fix what you broke.
- If requirements are ambiguous, ask one clear question instead of guessing.
- Never commit secrets, API keys or `.env` files. Use env vars and keep `.env.example` up to date.
- Do not add a new dependency when the standard library or an existing dependency already covers it.
- Ask before adding, removing or upgrading any dependency.
- Ask before changing database schemas, auth, payments or CI configuration.
- Never delete files, drop data or run destructive commands (`rm -rf`, `git push --force`, `DROP TABLE`) without explicit approval.
- Keep each change under ~200 changed lines where possible; split larger work into steps.

## Chrome Extension (MV3)

- Manifest V3 only. The background script is a service worker: no DOM, no `window`, and it can be terminated at any time.
- Persist state in `chrome.storage`, never in service worker globals.
- Request the minimum permissions and host permissions. Prefer `activeTab` and optional permissions.
- No remotely hosted code and no `eval`; all code ships in the package.
- Communicate between contexts with `chrome.runtime.sendMessage` / `onMessage` and typed message objects.
- Register event listeners at the top level of the service worker so they survive restarts.

## Tailwind CSS v4

- Tailwind v4 is configured in CSS: `@import "tailwindcss";` plus `@theme { ... }` for design tokens. Do not create a `tailwind.config.js` unless the project already has one.
- Use theme tokens (colors, spacing) instead of arbitrary values like `w-[37px]`.
- Build responsive layouts mobile-first with `sm:`, `md:`, `lg:` prefixes.
- Extract repeated class lists into components, not `@apply` chains.
- Support dark mode with the `dark:` variant when the project uses it.

## Zustand

- Keep stores small and split by domain.
- Select only what a component needs (`useStore((s) => s.count)`) to avoid unnecessary re-renders.
- Use Zustand for client/UI state only. Server data belongs in the data-fetching layer.

## Vitest

- Co-locate tests next to the code as `*.test.ts(x)`.
- Test behaviour through public APIs; for components use Testing Library queries by role/label.
- Mock network calls at the boundary (e.g. MSW) rather than mocking internal modules.
- Every bug fix adds a test that fails without the fix.

## Reference docs

- [Chrome extensions docs](https://developer.chrome.com/docs/extensions)
- [Tailwind CSS docs](https://tailwindcss.com/docs)
- [Zustand docs](https://zustand.docs.pmnd.rs)
- [Vitest docs](https://vitest.dev)