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.

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": "2024-02-16T13:00:00Z"
  }
}

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/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

Best Practices Summary

1. Consistency First: Maintain consistent naming, response formats, and patterns
2. Documentation: Provide comprehensive, up-to-date API documentation
3. Versioning: Plan for evolution with clear versioning strategies
4. Error Handling: Implement consistent, informative error responses
5. Security: Build security into every layer of the API
6. Performance: Design for scale and efficiency from the start
7. Backward Compatibility: Minimize breaking changes and provide migration paths
8. Testing: Implement comprehensive testing including contract testing
9. Monitoring: Add observability for API usage and performance
10. Developer Experience: Prioritize ease of use and clear documentation

Common Anti-Patterns to Avoid

1. Verb-based URLs: Use nouns for resources, not actions
2. Inconsistent Response Formats: Maintain standard response structures
3. Over-nesting: Avoid deeply nested resource hierarchies
4. Ignoring HTTP Status Codes: Use appropriate status codes for different scenarios
5. Poor Error Messages: Provide actionable, specific error information
6. Missing Pagination: Always paginate list endpoints
7. No Versioning Strategy: Plan for API evolution from day one
8. Exposing Internal Structure: Design APIs for external consumption, not internal convenience
9. Missing Rate Limiting: Protect your API from abuse and overload
10. Inadequate Testing: Test all aspects including error cases and edge conditions

Conclusion

The API Design Reviewer skill provides a comprehensive framework for building, reviewing, and maintaining high-quality REST APIs. By following these guidelines and using the provided tools, development teams can create APIs that are consistent, well-documented, secure, and maintainable.

Regular use of the linting, breaking change detection, and scoring tools ensures continuous improvement and helps maintain API quality throughout the development lifecycle.

Troubleshooting

/activate

POST /resource/{id}/activations

components/schemas

components/schemas

security

securitySchemes

components

paths

python -c "import yaml,json,sys; json.dump(yaml.safe_load(open(sys.argv[1])),open(sys.argv[2],'w'),indent=2)" spec.yaml spec.json

Cache-Control

limit

offset

cursor

Success Criteria

• Zero breaking changes detected between consecutive minor or patch releases (semver compliance)
• API consistency score (from

  api_scorecard.py

  ) above 90 across all reviewed specifications
• Overall scorecard grade of B or higher (80+) before any API ships to production
• 100% of endpoints include at least one success response and one error response definition
• All path segments follow kebab-case naming and all schema properties follow camelCase naming with zero linter errors
• Breaking change reports generated and reviewed for every PR that modifies an OpenAPI spec
• Documentation coverage score above 85%, meaning every operation has a summary and every schema has a description

Scope & Limitations

This skill covers:

• Linting OpenAPI 3.x and Swagger 2.0 JSON specifications against REST conventions
• Detecting breaking, potentially-breaking, and non-breaking changes between two spec versions
• Scoring API design quality across consistency, documentation, security, usability, and performance
• Generating actionable migration guides when breaking changes are found

This skill does NOT cover:

• Runtime API testing, load testing, or contract testing (see

  api-test-suite-builder

  )
• GraphQL, gRPC, or WebSocket API design review
• Auto-generation of OpenAPI specs from code or server stubs
• Authentication flow implementation or OAuth server configuration (see

  senior-security

  in engineering/)

Integration Points

engineering/api-test-suite-builder

engineering/changelog-generator

engineering/ci-cd-pipeline-builder

engineering/senior-backend

engineering/code-reviewer

engineering/release-manager

Tool Reference

api_linter.py

Purpose: Analyzes OpenAPI/Swagger JSON specifications for compliance with REST conventions and best practices. Checks naming conventions, HTTP method usage, URL structure, status codes, error formats, documentation completeness, and security configuration.

Usage:

python api_linter.py [OPTIONS] INPUT_FILE

Parameters:

input_file

--format

text

text

json

--raw-endpoints

--output

Example:

python api_linter.py openapi.json
python api_linter.py --format json openapi.json > report.json
python api_linter.py --raw-endpoints endpoints.json
python api_linter.py --output lint-report.txt openapi.json

Output Formats:

• text -- Human-readable report with issue breakdown by category, severity icons, suggestions, and a scoring summary. Exits with code 1 if any errors are found, 0 otherwise.
• json -- Machine-readable JSON object with

  summary

  (total_endpoints, endpoints_with_issues, total_issues, errors, warnings, info, score) and

  issues

  array (severity, category, message, path, suggestion).

breaking_change_detector.py

Purpose: Compares two versions of an OpenAPI JSON specification and detects breaking changes including removed endpoints, modified response structures, removed fields, type changes, new required fields, parameter changes, and status code changes. Generates migration guides for each breaking change.

Usage:

python breaking_change_detector.py [OPTIONS] OLD_SPEC NEW_SPEC

Parameters:

old_spec

new_spec

--format

text

text

json

--output

--exit-on-breaking

Example:

python breaking_change_detector.py v1.json v2.json
python breaking_change_detector.py --format json v1.json v2.json > changes.json
python breaking_change_detector.py --exit-on-breaking --output report.txt v1.json v2.json

Output Formats:

• text -- Human-readable report listing each change with its type (breaking, potentially_breaking, non_breaking, enhancement), severity (critical, high, medium, low, info), category, path, message, impact description, and migration guide.
• json -- Machine-readable JSON object with

  summary

  (total_changes, breaking_changes, potentially_breaking_changes, non_breaking_changes, enhancements, and per-severity counts) and

  changes

  array (changeType, severity, category, path, message, oldValue, newValue, migrationGuide, impactDescription).

api_scorecard.py

Purpose: Generates a comprehensive API design quality scorecard by evaluating an OpenAPI JSON specification across five weighted dimensions: Consistency (30%), Documentation (20%), Security (20%), Usability (15%), and Performance (15%). Produces letter grades (A-F) per category and overall, with actionable improvement recommendations.

Usage:

python api_scorecard.py [OPTIONS] SPEC_FILE

Parameters:

spec_file

--format

text

text

json

--output

--min-grade

A

B

C

D

F

Example:

python api_scorecard.py openapi.json
python api_scorecard.py --format json openapi.json > scorecard.json
python api_scorecard.py --min-grade B --output scorecard.txt openapi.json

Output Formats:

• text -- Human-readable scorecard showing API info, per-category scores with letter grades, issue counts, recommendations, and an overall weighted score with grade.
• json -- Machine-readable JSON object with

  apiInfo

  ,

  categoryScores

  (per category: score, maxScore, weight, letterGrade, weightedScore, issues, recommendations),

  overallScore

  ,

  overallGrade

  ,

  totalEndpoints

  , and

  topRecommendations

  .