Understanding APIs: From REST to GraphQL

Introduction

APIs are the backbone of modern software. They enable communication between applications, services, and systems. Understanding different API styles helps you build better integrations. This guide covers major API paradigms.

API Fundamentals

What Is an API

Application Programming Interface - a way for software to communicate.

Why APIs Matter

• Connect systems
• Enable integrations
• Mobile apps
• Microservices

REST APIs

Principles

• Stateless requests
• Resource-based URLs
• Standard HTTP methods
• JSON responses

REST URL Structure

GET    /api/users          # List users
GET    /api/users/123      # Get user
POST   /api/users          # Create user
PUT    /api/users/123      # Update user
DELETE /api/users/123      # Delete user

REST Example

// Request
GET /api/users/123

// Response
{
  "id": 123,
  "name": "John Doe",
  "email": "[email protected]",
  "created_at": "2025-01-15T10:30:00Z"
}

Best Practices

• Use nouns, not verbs
• Version your API
• Use proper status codes
• Support pagination

Status Codes

GraphQL

What Is GraphQL

Query language for APIs - clients request exactly what they need.

GraphQL vs REST

REST: /api/users/123 (returns all fields)
GraphQL: query { user(id: "123") { name, email } }

Schema Definition

type User {
  id: ID!
  name: String!
  email: String!
  posts: [Post!]!
}

type Post {
  id: ID!
  title: String!
  content: String
  author: User!
}

type Query {
  users: [User!]!
  user(id: ID!): User
}

type Mutation {
  createUser(input: CreateUserInput!): User!
}

When to Use GraphQL

• Multiple clients with different needs
• Complex data relationships
• Mobile apps (bandwidth)
• Rapid frontend iteration

gRPC

What Is gRPC

High-performance RPC using Protocol Buffers.

Protocol Buffers

syntax = "proto3";

message User {
  string id = 1;
  string name = 2;
  string email = 3;
}

service UserService {
  rpc GetUser (UserRequest) returns (User);
  rpc CreateUser (CreateUserRequest) returns (User);
}

When to Use gRPC

• High performance
• Microservices
• Real-time streaming
• Strong typing

WebSockets

What Are WebSockets

Bidirectional, persistent connections for real-time communication.

Use Cases

• Chat applications
• Live updates
• Gaming
• Collaborative editing

WebSocket Example

// Client
const ws = new WebSocket('wss://api.example.com/ws');

ws.onopen = () => {
  ws.send(JSON.stringify({ type: 'subscribe', channel: 'updates' }));
};

ws.onmessage = (event) => {
  const data = JSON.parse(event.data);
  console.log(data);
};

Webhooks

What Are Webhooks

HTTP callbacks - server notifies client of events.

Webhook Flow

Server → POST request → Client endpoint → Client processes

Webhook Security

• Verify signatures
• Use HTTPS
• Handle retries
• Idempotency

Choosing API Style

Hybrid Approaches

Many applications use multiple API styles:

• REST for CRUD
• GraphQL for queries
• WebSockets for real-time
• Webhooks for events

Best Practices

Security

• Authentication (OAuth, API keys)
• Rate limiting
• HTTPS always
• Input validation

Documentation

• OpenAPI/Swagger
• Examples
• Error codes
• Version history

Versioning

/api/v1/users
/api/v2/users

Conclusion

Each API style has strengths. REST is versatile, GraphQL flexible, gRPC performant. Choose based on your use case, client needs, and team expertise.

Resources

• RESTful Web APIs
• GraphQL
• gRPC
• MDN Web Docs - WebSockets