Design and Review HTTP APIs with old-coder-api

Where this fits

You have to add a /v2/orders endpoint or review a PR that changes an OpenAPI spec. Your agent needs to reason about whether renaming a field, adding a required header, or loosening pagination limits breaks existing consumers. old-coder-api scopes that reasoning to HTTP/JSON API contracts, so agents stop pattern-matching and start applying concrete compatibility rules.

Why agents benefit

• Catches breaking changes before they cause consumer incidents: field type shifts, required property additions, and default value changes are flagged against JSON consumer assumptions.
• Produces design reviews with boring, predictable API choices: idempotency keys, cursor pagination, rate-limit headers, and explicit versioning strategies.
• Keeps agents in scope: it knows it is not a gRPC/GraphQL/WebSockets compatibility checklist, so it won't hallucinate protocol-specific rules.
• Turns route diffs into actionable risks: before/after response shapes are compared directly instead of described vaguely.
• Speeds up API decision logs: agents can generate deprecation notices and migration paths with a clear rationale.

Practical scenarios

Adding an HTTP endpoint with sane defaults

An agent drafts a POST /webhooks endpoint and uses the skill to decide request/response shape, idempotency via Idempotency-Key, and 409 handling on replay.

Reviewing an OpenAPI spec PR

A developer asks whether this change breaks the mobile client. The agent reads the diff, identifies a changed $ref that introduces a required property, and recommends a compatible additive release.

Evaluating a public API deprecation

A team plans to remove a legacy endpoint. The agent uses the skill to propose a sunset header, 410 response, and migration mapping before the code change is written.

Add it to your agent workflow

Install with:

npx skills add AmazingAng/old-coder --skill old-coder-api

Then ask your agent: 'Use old-coder-api to review the route diff in spec.yaml and tell me which changes are breaking for JSON consumers.'

Compare before adopting

Before adding any skill, compare it against the alternatives. Look at the underlying source: old-coder-api is derived from Sean Goedecke's 'Everything I know about good API design,' so it inherits a strong point of view. Check maintenance freshness and the author's other work. Consider whether your agent already has API review skills, and whether those skills are protocol-aware or generic.

Why it is worth tracking

old-coder-api has 710 stars and a focused README that explicitly limits its scope to HTTP/JSON. That clarity is a good quality signal: the skill knows what it is for, and what it should not do. It is worth evaluating when you begin adding OpenAPI review, HTTP endpoint design, or API deprecation tasks to your agent toolbox. For more context, see https://www.openagentskill.com/skills/amazingang-old-coder-api