API Design Standards

This document outlines the standards and best practices for designing, developing, and maintaining APIs at Bayat.

Introduction

APIs (Application Programming Interfaces) are the foundation of modern software integration. This document provides guidelines for creating consistent, secure, and developer-friendly APIs.

API Types

REST APIs: Resource-oriented APIs using HTTP methods
GraphQL APIs: Query language for APIs with flexible data retrieval
gRPC APIs: High-performance RPC framework using Protocol Buffers
Webhook APIs: Event-driven APIs that deliver data via callbacks

API-First Approach

At Bayat, we follow an API-first approach:

Design the API before implementation
Use the API design as a contract between teams
Create mock implementations for early testing
Validate the API design with stakeholders
Implement the API according to the design

API Design Principles

Core Principles

Consistency: Follow consistent patterns across all APIs
Simplicity: Keep APIs simple and intuitive
Evolvability: Design APIs to evolve without breaking changes
Security: Build security into the API from the start
Performance: Optimize for efficient data transfer

Design Guidelines

Design for the API consumer's needs
Use domain-driven design principles
Create resource-oriented designs
Implement proper pagination for large collections
Support filtering, sorting, and field selection
Design for backward compatibility
Follow the principle of least surprise

REST API Guidelines

URL Structure

Use nouns, not verbs, for resource endpoints
Use plural nouns for collection resources
Use hierarchical structure for related resources
Use kebab-case for multi-word resource names

# Good
GET /users
GET /users/123
GET /users/123/orders
GET /product-categories

# Avoid
GET /getUsers
GET /user/123/getOrders
GET /productcategories

HTTP Methods

Use HTTP methods according to their defined semantics:

Method	Usage	Idempotent	Safe
GET	Retrieve a resource	Yes	Yes
POST	Create a resource	No	No
PUT	Replace a resource	Yes	No
PATCH	Partially update a resource	No	No
DELETE	Delete a resource	Yes	No

Status Codes

Use appropriate HTTP status codes:

2xx - Success
- 200 OK - Standard success response
- 201 Created - Resource created
- 204 No Content - Success with no response body
4xx - Client errors
- 400 Bad Request - Invalid request format
- 401 Unauthorized - Authentication required
- 403 Forbidden - Authenticated but not authorized
- 404 Not Found - Resource not found
- 422 Unprocessable Entity - Validation errors
5xx - Server errors
- 500 Internal Server Error - Unexpected server error
- 503 Service Unavailable - Service temporarily unavailable

Request and Response Format

Use JSON as the primary data format
Use consistent property naming (camelCase preferred)
Include content type headers (Content-Type: application/json)
Implement proper pagination for collections

// Collection response example
{
  "data": [
    { "id": 1, "name": "Item 1" },
    { "id": 2, "name": "Item 2" }
  ],
  "pagination": {
    "totalItems": 100,
    "totalPages": 10,
    "currentPage": 1,
    "pageSize": 10
  }
}

Filtering, Sorting, and Field Selection

Use query parameters for filtering: ?status=active
Support multiple filters: ?status=active&type=premium
Use query parameters for sorting: ?sort=name or ?sort=-createdAt (descending)
Support field selection: ?fields=id,name,email

GraphQL Guidelines

Schema Design

Use descriptive names for types, fields, and operations
Follow naming conventions consistently
Design for reusability with interfaces and unions
Implement proper pagination with connections pattern
Use enums for fields with predefined values

type User {
  id: ID!
  firstName: String!
  lastName: String!
  email: String!
  role: UserRole!
  createdAt: DateTime!
  updatedAt: DateTime!
  orders(first: Int, after: String): OrderConnection!
}

enum UserRole {
  ADMIN
  CUSTOMER
  GUEST
}

type OrderConnection {
  edges: [OrderEdge!]!
  pageInfo: PageInfo!
}

type OrderEdge {
  node: Order!
  cursor: String!
}

type PageInfo {
  hasNextPage: Boolean!
  hasPreviousPage: Boolean!
  startCursor: String
  endCursor: String
}

Query Design

Design queries around business use cases
Implement proper authorization checks
Use arguments for filtering and customization
Avoid deeply nested queries
Implement query complexity analysis

type Query {
  user(id: ID!): User
  users(
    filter: UserFilter
    orderBy: UserOrderBy
    first: Int
    after: String
  ): UserConnection!
}

input UserFilter {
  role: UserRole
  searchTerm: String
  isActive: Boolean
}

enum UserOrderBy {
  NAME_ASC
  NAME_DESC
  CREATED_AT_ASC
  CREATED_AT_DESC
}

Mutation Design

Use descriptive names for mutations
Return the modified resource and operation status
Group related input fields in input types
Implement proper validation
Return meaningful error messages

type Mutation {
  createUser(input: CreateUserInput!): CreateUserPayload!
  updateUser(input: UpdateUserInput!): UpdateUserPayload!
  deleteUser(id: ID!): DeleteUserPayload!
}

input CreateUserInput {
  firstName: String!
  lastName: String!
  email: String!
  role: UserRole!
}

type CreateUserPayload {
  user: User
  errors: [Error!]
}

type Error {
  path: String!
  message: String!
}

Performance Considerations

Implement dataloader pattern for batching requests
Use query complexity analysis to prevent abuse
Implement proper caching strategies
Consider persisted queries for production
Monitor and optimize resolver performance

API Versioning

Versioning Strategies

URI Path Versioning
- Include version in the URI path: /v1/users
- Simple to implement and understand
- Explicit version visibility
Query Parameter Versioning
- Use query parameter: /users?version=1
- Maintains clean resource URLs
- Less visible in documentation
Header Versioning
- Use custom header: Accept-Version: 1
- Keeps URLs clean
- More complex to test and debug
Content Negotiation
- Use Accept header: Accept: application/vnd.company.v1+json
- Standards-based approach
- More complex to implement

Versioning Policy

Use semantic versioning principles
Increment major version for breaking changes
Support at least one previous major version
Clearly document deprecation timelines
Provide migration guides for version upgrades

Authentication and Authorization

Authentication Methods

API Keys
- Simple to implement
- Suitable for server-to-server communication
- Less secure for client applications
OAuth 2.0
- Industry standard for authorization
- Support different grant types based on client type
- Implement proper token management
JWT (JSON Web Tokens)
- Stateless authentication
- Include minimal claims in tokens
- Implement proper signing and validation

Authorization

Implement role-based access control (RBAC)
Use attribute-based access control (ABAC) for complex scenarios
Check permissions at the resource level
Document permission requirements for each endpoint
Return appropriate status codes (401 vs 403)

Security Best Practices

Use HTTPS for all API endpoints
Implement proper CORS policies
Set appropriate token expiration times
Implement rate limiting and throttling
Monitor for suspicious activities

Error Handling

Error Response Format

Use a consistent error response format:

{
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "The request contains invalid parameters",
    "details": [
      {
        "field": "email",
        "message": "Must be a valid email address"
      },
      {
        "field": "password",
        "message": "Must be at least 8 characters long"
      }
    ]
  }
}

Error Types

Validation errors: Issues with request data
Authentication errors: Issues with authentication
Authorization errors: Permission issues
Resource errors: Resource not found or conflict
Server errors: Unexpected server issues

Error Handling Best Practices

Use appropriate HTTP status codes
Provide clear error messages
Include error codes for programmatic handling
Add details for validation errors
Avoid exposing sensitive information in errors
Log errors with appropriate context

Documentation

API Documentation Standards

Use OpenAPI/Swagger for REST APIs
Use GraphQL introspection and schema documentation
Include detailed descriptions for all endpoints
Document request and response formats
Provide examples for common operations
Document error responses and codes

Documentation Tools

Use Swagger UI for REST API documentation
Use GraphQL Playground or GraphiQL for GraphQL APIs
Implement documentation generation in CI/CD pipeline
Keep documentation in sync with implementation

Developer Experience

Provide quickstart guides
Include code examples in multiple languages
Offer SDKs for common platforms
Provide interactive API explorers
Document rate limits and quotas

Performance

Performance Optimization

Implement proper caching strategies
Use compression for responses
Optimize database queries
Implement pagination for large collections
Support partial responses and field selection

Caching

Use ETags for cache validation
Implement Cache-Control headers
Use CDN for public resources
Implement application-level caching
Document caching behavior

Rate Limiting

Implement rate limiting for all APIs
Use token bucket or leaky bucket algorithms
Include rate limit headers in responses:
- X-RateLimit-Limit
- X-RateLimit-Remaining
- X-RateLimit-Reset
Document rate limits in API documentation

Security

Security Checklist

Enforce HTTPS for all endpoints
Implement proper authentication and authorization
Validate all input data
Protect against injection attacks
Implement rate limiting and throttling
Use appropriate CORS headers
Protect against common API vulnerabilities

OWASP API Security

Follow the OWASP API Security Top 10:

Broken Object Level Authorization
Broken User Authentication
Excessive Data Exposure
Lack of Resources & Rate Limiting
Broken Function Level Authorization
Mass Assignment
Security Misconfiguration
Injection
Improper Assets Management
Insufficient Logging & Monitoring

Security Headers

Implement appropriate security headers:

Strict-Transport-Security
Content-Security-Policy
X-Content-Type-Options
X-Frame-Options
X-XSS-Protection

Testing

Testing Strategy

Implement unit tests for API logic
Create integration tests for API endpoints
Perform contract testing
Conduct security testing
Implement performance testing

Test Automation

Automate API tests in CI/CD pipeline
Use tools like Postman, REST Assured, or Supertest
Implement test data management
Create test environments that mirror production
Monitor test coverage

Contract Testing

Use tools like Pact for contract testing
Define consumer-driven contracts
Verify provider implementation against contracts
Integrate contract tests in CI/CD pipeline

Monitoring

Monitoring Metrics

Track request rates and response times
Monitor error rates and types
Track API usage by endpoint
Monitor authentication failures
Track rate limit hits

Logging

Implement structured logging
Include correlation IDs for request tracing
Log request and response metadata
Implement proper log levels
Centralize log collection and analysis

Alerting

Set up alerts for critical errors
Monitor for unusual traffic patterns
Alert on security incidents
Implement on-call procedures
Document incident response process

Version History

Version	Date	Description
1.0	2025-03-20	Initial version

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