What Is an API? A Beginner's Guide for Web Developers

When you open a weather app, how does it get data from the meteorology service? Or when you make a payment on an e-commerce site, how does it communicate with the bank? The answer: API.

What Is an API?

API (Application Programming Interface) is an interface that enables different software systems to communicate with each other. Simply put, it's a door through which one software can tell another "do this" or "give me this data."

Real-Life Analogy

Think of an API like a waiter:

• You (customer) = Your application
• Menu = API documentation
• Waiter = API
• Kitchen = Server/database

You choose from the menu, the waiter takes your order to the kitchen, the kitchen prepares it, and the waiter brings it back.

Types of APIs

1. REST API

The most common API type. Works over the HTTP protocol.

Basic HTTP Methods:

• GET — Read data (fetch product list)
• POST — Create new data (register new user)
• PUT — Update data (edit profile)
• DELETE — Delete data (remove account)

Example:

GET    /api/products        → List all products
GET    /api/products/42     → Get product #42
POST   /api/products        → Add new product
PUT    /api/products/42     → Update product #42
DELETE /api/products/42     → Delete product #42

2. GraphQL

A query language developed by Facebook, working through a single endpoint.

Advantages:

• Request exactly the data you need (no over-fetching)
• Pull from multiple sources in a single request
• Strong type system

3. WebSocket

Real-time, bidirectional communication:

• Chat applications
• Live notifications
• Stock market data
• Multiplayer games

4. Webhook

Event-based notification system:

• Notification when payment completes
• Email when new order arrives
• CI/CD pipeline triggering

How Does an API Work?

1. Client (Frontend) → Sends request
2. API → Receives and validates request
3. Server → Processes request
4. Database → Reads/writes data
5. Server → Creates response
6. API → Returns response
7. Client → Displays response

API Security

Authentication Methods:

• API Key — Simple but limited security
• OAuth 2.0 — Industry standard (Google, Facebook login)
• JWT — Token-based authentication
• Basic Auth — Username + password (with HTTPS)

Security Tips:

• Always use HTTPS
• Implement rate limiting
• Validate inputs
• Never store API keys in source code
• Set CORS policies

Popular Public APIs

| API | Use | Price | |-----|-----|-------| | Google Maps | Maps, location | Freemium | | OpenWeatherMap | Weather | Freemium | | Stripe | Payment processing | Per transaction | | Twilio | SMS, calls | Per usage | | OpenAI | Artificial intelligence | Per token |

API Development Tools

• Postman — API testing and documentation
• Swagger/OpenAPI — API specification standard
• Insomnia — REST client
• cURL — Command-line HTTP client

Conclusion

APIs are the building blocks of the modern web. Almost every application you use today communicates with dozens of APIs behind the scenes. Understanding APIs is a critical step in your web development journey.

If you'd like to build professional web applications with API integrations, get in touch: info@cagribilgehan.com. Check out my projects: cagribilgehan.com