---
name: api-designer
description: 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.
license: MIT
metadata:
author: https://github.com/Jeffallan
version: "1.1.0"
domain: api-architecture
triggers: API design, REST API, OpenAPI, API specification, API architecture, resource modeling, API versioning, GraphQL schema, API documentation
role: architect
scope: design
output-format: specification
related-skills: graphql-architect, fastapi-expert, nestjs-expert, spring-boot-engineer, security-reviewer
---
# 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:
| 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+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](https://jeffallan.github.io/claude-skills/skills/api-architecture/api-designer/)