API Design Reviewer

Tier: POWERFUL

Category: Engineering / Architecture

Maintainer: Claude Skills Team

Overview

The API Design Reviewer skill provides comprehensive analysis and review of API designs, focusing on REST conventions, best practices, and industry standards. This skill helps engineering teams build consistent, maintainable, and well-designed APIs through automated linting, breaking change detection, and design scorecards.

Quick Start — run the tools first

# 1. Lint an OpenAPI/Swagger spec for convention violations

python3 scripts/api_linter.py openapi.json --format json -o lint.json

# 2. Detect breaking changes between two spec versions (gate: exits non-zero with --exit-on-breaking)

python3 scripts/breaking_change_detector.py openapi-v1.json openapi-v2.json --format json --exit-on-breaking -o breaking.json

3. Score overall design quality (gate: --min-grade fails below threshold)

python3 scripts/api_scorecard.py openapi.json --format json --min-grade B -o scorecard.json

Review flow: run all three, report linter findings + breaking changes + grade to the user, fix, then re-run until the linter is clean, `--exit-on-breaking` passes (or breaking changes are version-bumped), and the scorecard meets the agreed `--min-grade`. Never sign off an API review on prose alone — attach the tool outputs.

## Core Capabilities

### 1. API Linting and Convention Analysis

- **Resource Naming Conventions**: Enforces kebab-case for resources, camelCase for fields

- **HTTP Method Usage**: Validates proper use of GET, POST, PUT, PATCH, DELETE

- **URL Structure**: Analyzes endpoint patterns for consistency and RESTful design

- **Status Code Compliance**: Ensures appropriate HTTP status codes are used

- **Error Response Formats**: Validates consistent error response structures

- **Documentation Coverage**: Checks for missing descriptions and documentation gaps

### 2. Breaking Change Detection

- **Endpoint Removal**: Detects removed or deprecated endpoints

- **Response Shape Changes**: Identifies modifications to response structures

- **Field Removal**: Tracks removed or renamed fields in API responses

- **Type Changes**: Catches field type modifications that could break clients

- **Required Field Additions**: Flags new required fields that could break existing integrations

- **Status Code Changes**: Detects changes to expected status codes

### 3. API Design Scoring and Assessment

- **Consistency Analysis** (30%): Evaluates naming conventions, response patterns, and structural consistency

- **Documentation Quality** (20%): Assesses completeness and clarity of API documentation

- **Security Implementation** (20%): Reviews authentication, authorization, and security headers

- **Usability Design** (15%): Analyzes ease of use, discoverability, and developer experience

- **Performance Patterns** (15%): Evaluates caching, pagination, and efficiency patterns

## REST Design Principles

### Resource Naming Conventions

✅ Good Examples:

• /api/v1/users

• /api/v1/user-profiles

• /api/v1/orders/123/line-items

❌ Bad Examples:

• /api/v1/getUsers

• /api/v1/user_profiles

• /api/v1/orders/123/lineItems

### HTTP Method Usage

- **GET**: Retrieve resources (safe, idempotent)

- **POST**: Create new resources (not idempotent)

- **PUT**: Replace entire resources (idempotent)

- **PATCH**: Partial resource updates (not necessarily idempotent)

- **DELETE**: Remove resources (idempotent)

### URL Structure Best Practices

Collection Resources: /api/v1/users

Individual Resources: /api/v1/users/123

Nested Resources: /api/v1/users/123/orders

Actions: /api/v1/users/123/activate (POST)

Filtering: /api/v1/users?status=active&role=admin

## Versioning Strategies

### 1. URL Versioning (Recommended)

/api/v1/users

/api/v2/users

**Pros**: Clear, explicit, easy to route

**Cons**: URL proliferation, caching complexity

### 2. Header Versioning

GET /api/users

Accept: application/vnd.api+json;version=1

**Pros**: Clean URLs, content negotiation

**Cons**: Less visible, harder to test manually

### 3. Media Type Versioning

GET /api/users

Accept: application/vnd.myapi.v1+json

**Pros**: RESTful, supports multiple representations

**Cons**: Complex, harder to implement

### 4. Query Parameter Versioning

/api/users?version=1

**Pros**: Simple to implement

**Cons**: Not RESTful, can be ignored

## Pagination Patterns

### Offset-Based Pagination

{

"data": [...],

"pagination": {

"offset": 20,

"limit": 10,

"total": 150,

"hasMore": true

}

}

### Cursor-Based Pagination

{

"data": [...],

"pagination": {

"nextCursor": "eyJpZCI6MTIzfQ==",

"hasMore": true

}

}

### Page-Based Pagination

{

"data": [...],

"pagination": {

"page": 3,

"pageSize": 10,

"totalPages": 15,

"totalItems": 150

}

}

## Error Response Formats

### Standard Error Structure

{

"error": {

"code": "VALIDATION_ERROR",

"message": "The request contains invalid parameters",

"details": [

{

"field": "email",

"code": "INVALID_FORMAT",

"message": "Email address is not valid"

}

],

"requestId": "req-123456",

"timestamp": "2026-02-16T13:00:00Z"

}

}

### HTTP Status Code Usage

- **400 Bad Request**: Invalid request syntax or parameters

- **401 Unauthorized**: Authentication required

- **403 Forbidden**: Access denied (authenticated but not authorized)

- **404 Not Found**: Resource not found

- **409 Conflict**: Resource conflict (duplicate, version mismatch)

- **422 Unprocessable Entity**: Valid syntax but semantic errors

- **429 Too Many Requests**: Rate limit exceeded

- **500 Internal Server Error**: Unexpected server error

## Authentication and Authorization Patterns

### Bearer Token Authentication

Authorization: Bearer <token>

### API Key Authentication

X-API-Key: <api-key>

Authorization: Api-Key <api-key>

### OAuth 2.0 Flow

Authorization: Bearer <oauth-access-token>

### Role-Based Access Control (RBAC)

{

"user": {

"id": "123",

"roles": ["admin", "editor"],

"permissions": ["read:users", "write:orders"]

}

}

## Rate Limiting Implementation

### Headers

X-RateLimit-Limit: 1000

X-RateLimit-Remaining: 999

X-RateLimit-Reset: 1640995200

### Response on Limit Exceeded

{

"error": {

"code": "RATE_LIMIT_EXCEEDED",

"message": "Too many requests",

"retryAfter": 3600

}

}

## HATEOAS (Hypermedia as the Engine of Application State)

### Example Implementation

{

"id": "123",

"name": "John Doe",

"email": "john@example.com",

"_links": {

"self": { "href": "/api/v1/users/123" },

"orders": { "href": "/api/v1/users/123/orders" },

"profile": { "href": "/api/v1/users/123/profile" },

"deactivate": {

"href": "/api/v1/users/123/deactivate",

"method": "POST"

}

}

}

## Idempotency

### Idempotent Methods

- **GET**: Always safe and idempotent

- **PUT**: Should be idempotent (replace entire resource)

- **DELETE**: Should be idempotent (same result)

- **PATCH**: May or may not be idempotent

### Idempotency Keys

POST /api/v1/payments

Idempotency-Key: 123e4567-e89b-12d3-a456-426614174000

## Backward Compatibility Guidelines

### Safe Changes (Non-Breaking)

- Adding optional fields to requests

- Adding fields to responses

- Adding new endpoints

- Making required fields optional

- Adding new enum values (with graceful handling)

### Breaking Changes (Require Version Bump)

- Removing fields from responses

- Making optional fields required

- Changing field types

- Removing endpoints

- Changing URL structures

- Modifying error response formats

## OpenAPI/Swagger Validation

### Required Components

- **API Information**: Title, description, version

- **Server Information**: Base URLs and descriptions

- **Path Definitions**: All endpoints with methods

- **Parameter Definitions**: Query, path, header parameters

- **Request/Response Schemas**: Complete data models

- **Security Definitions**: Authentication schemes

- **Error Responses**: Standard error formats

### Best Practices

- Use consistent naming conventions

- Provide detailed descriptions for all components

- Include examples for complex objects

- Define reusable components and schemas

- Validate against OpenAPI specification

## Performance Considerations

### Caching Strategies

Cache-Control: public, max-age=3600

ETag: "123456789"

Last-Modified: Wed, 21 Oct 2015 07:28:00 GMT

### Efficient Data Transfer

- Use appropriate HTTP methods

- Implement field selection (`?fields=id,name,email`)

- Support compression (gzip)

- Implement efficient pagination

- Use ETags for conditional requests

### Resource Optimization

- Avoid N+1 queries

- Implement batch operations

- Use async processing for heavy operations

- Support partial updates (PATCH)

## Security Best Practices

### Input Validation

- Validate all input parameters

- Sanitize user data

- Use parameterized queries

- Implement request size limits

### Authentication Security

- Use HTTPS everywhere

- Implement secure token storage

- Support token expiration and refresh

- Use strong authentication mechanisms

### Authorization Controls

- Implement principle of least privilege

- Use resource-based permissions

- Support fine-grained access control

- Audit access patterns

## Tools and Scripts

### api_linter.py

Analyzes API specifications for compliance with REST conventions and best practices.

**Features:**

- OpenAPI/Swagger spec validation

- Naming convention checks

- HTTP method usage validation

- Error format consistency

- Documentation completeness analysis

### breaking_change_detector.py

Compares API specification versions to identify breaking changes.

**Features:**

- Endpoint comparison

- Schema change detection

- Field removal/modification tracking

- Migration guide generation

- Impact severity assessment

### api_scorecard.py

Provides comprehensive scoring of API design quality.

**Features:**

- Multi-dimensional scoring

- Detailed improvement recommendations

- Letter grade assessment (A-F)

- Benchmark comparisons

- Progress tracking

## Integration Examples

### CI/CD Integration

• name: "api-linting"

run: python scripts/api_linter.py openapi.json

• name: "breaking-change-detection"

run: python scripts/breaking_change_detector.py openapi-v1.json openapi-v2.json

• name: "api-scorecard"

run: python scripts/api_scorecard.py openapi.json

### Pre-commit Hooks

#!/bin/bash

python engineering/skills/api-design-reviewer/scripts/api_linter.py api/openapi.json

if [ $? -ne 0 ]; then

echo "API linting failed. Please fix the issues before committing."

exit 1

fi