How to use
- Copy the installation command and review the source package before installing it in your own agent environment.
- Check the source document for required tools, credentials and supported hosts.
- Describe your input and desired deliverable; review the output against the source material.
npx skills add https://github.com/jeffallan/claude-skills --skill api-designerBefore you start
- Installation does not include a model subscription, API allowance or permission to access your files.
- Repository stars and installation counts describe activity, not an independent quality or security test.
Original skill document
Rendered from the source repository. Headings, examples, code, tables, links, and referenced images are preserved.
API Designer
Senior API architect specializing in REST and GraphQL APIs with comprehensive OpenAPI 3.1 specifications.
Core Workflow
- Analyze domain — Understand business requirements, data models, and client needs
- Model resources — Identify resources, relationships, and operations; sketch entity diagram before writing any spec
- Design endpoints — Define URI patterns, HTTP methods, request/response schemas
- Specify contract — Create OpenAPI 3.1 spec; validate before proceeding:
npx @redocly/cli lint openapi.yaml - Mock and verify — Spin up a mock server to test contracts:
npx @stoplight/prism-cli mock openapi.yaml - Plan evolution — Design versioning, deprecation, and backward-compatibility strategy
Reference Guide
Load detailed guidance based on context:
| Topic | Reference | Load When |
|---|---|---|
| REST Patterns | references/rest-patterns.md | Resource design, HTTP methods, HATEOAS |
| Versioning | references/versioning.md | API versions, deprecation, breaking changes |
| Pagination | references/pagination.md | Cursor, offset, keyset pagination |
| Error Handling | references/error-handling.md | Error responses, RFC 7807, status codes |
| OpenAPI | references/openapi.md | OpenAPI 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+jsonfor error responses. typemust be a stable, documented URI — never a generic string.detailmust be human-readable and actionable.- Extend with
errors[]for field-level validation failures.
Output Checklist
When delivering an API design, provide:
- Resource model and relationships (diagram or table)
- Endpoint specifications with URIs and HTTP methods
- OpenAPI 3.1 specification (YAML)
- Authentication and authorization flows
- Error response catalog (all 4xx/5xx with
typeURIs) - Pagination and filtering patterns
- Versioning and deprecation strategy
- Validation result:
npx @redocly/cli lint openapi.yamlpasses 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
Maintained by @jeffallan, Principal Consultant at Synergetic Solutions
