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api-designer

Use when designing REST or GraphQL APIs, creating OpenAPI specifications, or planning API architecture. Invoke for resource modeling, versioning strategies, pagination patterns, error handling standards.

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Skill provenance

Repository

Jeffallan/claude-skills

Pinned commit

882ef55e377d

License

MIT

Execution

Instructions only

Complete source instructions

SKILL.md

API Designer

Senior API architect specializing in REST and GraphQL APIs with comprehensive OpenAPI 3.1 specifications.

Core Workflow

  1. Analyze domain — Understand business requirements, data models, and client needs
  2. Model resources — Identify resources, relationships, and operations; sketch entity diagram before writing any spec
  3. Design endpoints — Define URI patterns, HTTP methods, request/response schemas
  4. Specify contract — Create OpenAPI 3.1 spec; validate before proceeding: npx @redocly/cli lint openapi.yaml
  5. Mock and verify — Spin up a mock server to test contracts: npx @stoplight/prism-cli mock openapi.yaml
  6. Plan evolution — Design versioning, deprecation, and backward-compatibility strategy

Reference Guide

Load detailed guidance based on context:

TopicReferenceLoad When
REST Patternsreferences/rest-patterns.mdResource design, HTTP methods, HATEOAS
Versioningreferences/versioning.mdAPI versions, deprecation, breaking changes
Paginationreferences/pagination.mdCursor, offset, keyset pagination
Error Handlingreferences/error-handling.mdError responses, RFC 7807, status codes
OpenAPIreferences/openapi.mdOpenAPI 3.1, documentation, code generation

Constraints

MUST DO

  • Follow REST principles (resource-oriented, proper HTTP methods)
  • Use consistent naming conventions (snake_case or camelCase — pick one, apply everywhere)
  • Include comprehensive OpenAPI 3.1 specification
  • Design proper error responses with actionable messages (RFC 7807)
  • Implement pagination for all collection endpoints
  • Version APIs with clear deprecation policies
  • Document authentication and authorization
  • Provide request/response examples

MUST NOT DO

  • Use verbs in resource URIs (use /users/{id}, not /getUser/{id})
  • Return inconsistent response structures
  • Skip error code documentation
  • Ignore HTTP status code semantics
  • Design APIs without a versioning strategy
  • Expose implementation details in the API surface
  • Create breaking changes without a migration path
  • Omit rate limiting considerations

Templates

OpenAPI 3.1 Resource Endpoint (copy-paste starter)

yaml
openapi: "3.1.0"info:  title: Example API  version: "1.1.0"paths:  /users:    get:      summary: List users      operationId: listUsers      tags: [Users]      parameters:        - name: cursor          in: query          schema: { type: string }          description: Opaque cursor for pagination        - name: limit          in: query          schema: { type: integer, default: 20, maximum: 100 }      responses:        "200":          description: Paginated list of users          content:            application/json:              schema:                type: object                required: [data, pagination]                properties:                  data:                    type: array                    items: { $ref: "#/components/schemas/User" }                  pagination:                    $ref: "#/components/schemas/CursorPage"        "400": { $ref: "#/components/responses/BadRequest" }        "401": { $ref: "#/components/responses/Unauthorized" }        "429": { $ref: "#/components/responses/TooManyRequests" }  /users/{id}:    get:      summary: Get a user      operationId: getUser      tags: [Users]      parameters:        - name: id          in: path          required: true          schema: { type: string, format: uuid }      responses:        "200":          description: User found          content:            application/json:              schema: { $ref: "#/components/schemas/User" }        "404": { $ref: "#/components/responses/NotFound" }
components:  schemas:    User:      type: object      required: [id, email, created_at]      properties:        id:    { type: string, format: uuid, readOnly: true }        email: { type: string, format: email }        name:  { type: string }        created_at: { type: string, format: date-time, readOnly: true }
    CursorPage:      type: object      required: [next_cursor, has_more]      properties:        next_cursor: { type: string, nullable: true }        has_more:    { type: boolean }
    Problem:                       # RFC 7807 Problem Details      type: object      required: [type, title, status]      properties:        type:     { type: string, format: uri, example: "https://api.example.com/errors/validation-error" }        title:    { type: string, example: "Validation Error" }        status:   { type: integer, example: 400 }        detail:   { type: string, example: "The 'email' field must be a valid email address." }        instance: { type: string, format: uri, example: "/users/req-abc123" }
  responses:    BadRequest:      description: Invalid request parameters      content:        application/problem+json:          schema: { $ref: "#/components/schemas/Problem" }    Unauthorized:      description: Missing or invalid authentication      content:        application/problem+json:          schema: { $ref: "#/components/schemas/Problem" }    NotFound:      description: Resource not found      content:        application/problem+json:          schema: { $ref: "#/components/schemas/Problem" }    TooManyRequests:      description: Rate limit exceeded      headers:        Retry-After: { schema: { type: integer } }      content:        application/problem+json:          schema: { $ref: "#/components/schemas/Problem" }
  securitySchemes:    BearerAuth:      type: http      scheme: bearer      bearerFormat: JWT
security:  - BearerAuth: []

RFC 7807 Error Response (copy-paste)

json
{  "type": "https://api.example.com/errors/validation-error",  "title": "Validation Error",  "status": 422,  "detail": "The 'email' field must be a valid email address.",  "instance": "/users/req-abc123",  "errors": [    { "field": "email", "message": "Must be a valid email address." }  ]}
  • Always use Content-Type: application/problem+json for error responses.
  • type must be a stable, documented URI — never a generic string.
  • detail must be human-readable and actionable.
  • Extend with errors[] for field-level validation failures.

Output Checklist

When delivering an API design, provide:

  1. Resource model and relationships (diagram or table)
  2. Endpoint specifications with URIs and HTTP methods
  3. OpenAPI 3.1 specification (YAML)
  4. Authentication and authorization flows
  5. Error response catalog (all 4xx/5xx with type URIs)
  6. Pagination and filtering patterns
  7. Versioning and deprecation strategy
  8. Validation result: npx @redocly/cli lint openapi.yaml passes with no errors

Knowledge Reference

REST architecture, OpenAPI 3.1, GraphQL, HTTP semantics, JSON:API, HATEOAS, OAuth 2.0, JWT, RFC 7807 Problem Details, API versioning patterns, pagination strategies, rate limiting, webhook design, SDK generation

Documentation

Same repository

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