Lists multiple specific concrete actions: 'safe retries for POST endpoints', 'idempotency keys', and 'preventing duplicate orders'. These are concrete, actionable capabilities.

Clearly answers both what ('safe retries for POST endpoints, idempotency keys, preventing duplicate orders') and when ('Apply AUTOMATICALLY whenever building any POST endpoint that creates resources or triggers side effects').

Includes natural keywords users would say: 'idempotent', 'API', 'retries', 'POST endpoints', 'idempotency keys', 'duplicate orders'. These cover both technical terms and problem descriptions users might mention.

Clear niche focused specifically on idempotent API design with distinct triggers like 'idempotency keys', 'POST endpoints', 'duplicate orders'. Unlikely to conflict with general API or coding skills.

The content is comprehensive but includes some unnecessary explanation (e.g., explaining what GET/PUT/DELETE idempotency means, the ASCII diagram of the problem). Some sections could be tightened, though most content earns its place with concrete examples.

Excellent executable code examples throughout: complete TypeScript middleware, client-side fetch with retry handling, SQL schema with constraints, and database error handling. All code is copy-paste ready with proper error handling.

Clear multi-step workflow with explicit validation checkpoints: lock-before-process sequence, 409 handling for concurrent requests, and a comprehensive checklist at the end. The 'How it works' section clearly sequences the decision tree.

Content is well-organized with clear sections, but it's a long monolithic document (~300 lines). The verifier references at the end are good, but detailed implementations (server middleware, client code, database schema) could be split into separate reference files.