API development is one of the areas where SKILL.md skills provide the most value. APIs have established patterns and conventions that are easy to get wrong — proper error handling, consistent response formats, authentication flows, rate limiting, and documentation. A good skill ensures your agent follows these conventions every time.
Quick Answer: The best AI agent skills for API development are REST API design, GraphQL, authentication, API documentation, and rate limiting/security. These skills ensure agents follow conventions, handle security, and generate proper documentation.
REST API design skills
The most useful REST skills encode API design standards: proper HTTP method usage, consistent URL structures, standardized error response formats, pagination patterns, and HATEOAS links. Without a skill, agents tend to generate APIs that work but don't follow conventions — returning 200 for everything, inconsistent naming, missing pagination.
A good REST skill produces endpoints with proper status codes (201 for creation, 204 for deletion, 422 for validation errors), consistent JSON envelope structures, and cursor-based pagination out of the box.
GraphQL skills
GraphQL has its own set of patterns that differ significantly from REST. A GraphQL skill handles schema design (types, queries, mutations, subscriptions), resolver patterns, DataLoader usage for the N+1 problem, and error handling via the errors array rather than HTTP status codes.
These skills are particularly valuable because GraphQL has more ways to do things wrong — circular references, over-fetching at the schema level, missing authorization checks on nested resolvers.
Authentication skills
Auth is where most API security issues originate. An authentication skill handles JWT token generation and validation, OAuth 2.0 flows, API key management, rate limiting per key, and proper secret storage. It ensures your agent never hardcodes secrets, always validates tokens server-side, and implements proper CORS headers.
API documentation skills
The best API documentation skills generate OpenAPI/Swagger specs alongside your implementation code, ensuring they stay synchronized. They handle parameter descriptions, example request/response bodies, authentication requirements, and error response documentation.
Rate limiting and security
Skills for rate limiting implement token bucket or sliding window algorithms, handle distributed rate limiting with Redis, and return proper 429 responses with Retry-After headers. Security skills add input validation, SQL injection prevention, and request size limits.
Finding API skills
Browse API development skills on Agensi — the API Development category has skills for REST, GraphQL, and API security across all major frameworks.