API Design

--- name: api-design type: workflow description: "Defines REST and GraphQL API contracts including endpoints, request/response schemas, auth flows, and versioning strategy. Use when designing a new API, reviewing an API spec, or when the user mentions API design, OpenAPI, or endpoint contracts." argument-hint: "[path-to-api-spec-or-route-files]" user-invocable: true allowed-tools: Read, Glob, Grep, WebSearch effort: 3 when_to_use: "When designing or reviewing REST/GraphQL API contracts, endpoint naming, schemas, or versioning"

When this skill is invoked:

1. Read the target API spec or route files in full.

   For API design in an existing domain, SHOULD also inspect docs/technical/API.md, related design/specs/*, related design/contracts/* if present, and recent relevant ledger entries via /trace-history. This is advisory unless the change is an ADR, coordination-rule change, high-risk retry, or protocol removal.

2. Identify the API type (REST, GraphQL, WebSocket) and apply appropriate standards.

3. Evaluate REST design quality (if REST):

   • Resources use nouns, not verbs (/users, not /getUsers)
   • Correct HTTP methods (GET=read, POST=create, PUT/PATCH=update, DELETE=remove)
   • Consistent plural resource naming (/users, /orders)
   • Nested resources have max 2-3 levels of depth
   • Query parameters used for filtering, sorting, pagination (not in path)

4. Evaluate request/response schemas:

   • All inputs are validated and typed
   • Responses are consistent in structure (envelope format if used)
   • Pagination is consistent (cursor or page-based, not mixed)
   • Timestamps in ISO 8601 (UTC)
   • Money values in smallest currency unit (cents), not floats

5. Evaluate authentication & authorization:

   • Every endpoint has explicit auth requirement documented
   • Authorization is checked server-side, not just on the client
   • Sensitive data not leaked in error messages

6. Evaluate error responses:

   • Consistent error format (RFC 7807 Problem Details recommended)
   • HTTP status codes used correctly (400 for client errors, 500 for server)
   • Error messages are user-safe (no stack traces, SQL errors)

7. Evaluate versioning & backward compatibility:

   • Breaking changes require a version bump
   • Deprecation policy documented
   • Clients can negotiate API version

8. Output the review:

## API Design Review: [API/Endpoint Name]

### REST Design: [CLEAN / ISSUES FOUND]
[List specific issues with examples]

### Schema Quality: [CLEAN / ISSUES FOUND]
[List schema inconsistencies or problems]

### Auth & Security: [SECURE / ISSUES FOUND]
[List authentication and authorization issues]

### Error Handling: [CONSISTENT / ISSUES FOUND]
[List error response problems]

### Versioning: [HANDLED / UNADDRESSED]
[Notes on breaking change risk]

### Positive Observations
[What is well-designed]

### Required Changes
[Must-fix items before shipping]

### Suggestions
[Nice-to-have improvements]

### Verdict: [APPROVED / APPROVED WITH SUGGESTIONS / CHANGES REQUIRED]

Protocol

• Question: Auto-starts from argument (path to API spec or route files); no clarification needed
• Options: Skip — single review path
• Decision: Skip — verdict is advisory
• Draft: Full review report shown in conversation only
• Approval: Skip — read-only; no files written

Output

Deliver exactly:

• Endpoint compliance score (X/Y checks passing across naming, methods, validation, errors)
• Security issues with severity — CRITICAL / HIGH / MEDIUM (or "None")
• Required changes — must fix before shipping (or "None")
• Verdict: APPROVED / APPROVED WITH SUGGESTIONS / CHANGES REQUIRED