diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 0000000..c1f3f20
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1,30 @@
+# Google Apps Script — Claude Code Project Context
+
+This file provides Claude Code-specific instructions. For comprehensive agent guidelines (repo layout, setup, testing, code style, PR reviews), see [AGENTS.md](./AGENTS.md).
+
+## Quick Reference
+
+- **Install:** `npm install`
+- **Test (includes coverage):** `npm test`
+- **Lint + format check:** `npm run check`
+- **Format:** `npx prettier --write .`
+
+## Key Rules
+
+1. **TDD is mandatory** — write tests before implementation, include tests in the same PR
+2. **Coverage thresholds** — 100% lines, 95% statements/functions, 85% branches
+3. **Avoid coverage-ignore comments and `.skip()`** — only use in rare, unavoidable cases (per AGENTS.md) with clear justification
+4. **GAS testing pattern** — extract logic to `src/index.js` with `module.exports`, inject GAS services as parameters
+5. **Always run** `npx prettier --write .` before committing — pre-commit hooks don't run in agent sessions
+6. **Always run** `npm run check` (lint + format) and `npm test` (tests + coverage) before committing
+
+## Architecture
+
+- `src/<script-name>/code.gs` — Apps Script entry point
+- `src/<script-name>/config.gs` — configuration
+- `src/<script-name>/src/index.js` — testable extracted logic
+- `src/<script-name>/tests/` — Jest unit tests
+- `src/gas-utils.js` — shared utilities
+- `test-utils/` — shared Jest helpers/mocks
+
+See [AGENTS.md](./AGENTS.md) for full details.