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What Is an API?

An API (Application Programming Interface) is an interface that enables different software applications to communicate with each other. Think of it like a waiter in a restaurant: you (the client) can't go directly to the kitchen (server), but the waiter (API) takes your order and brings you your food.

At BUZ Yazılım, we have developed and integrated hundreds of APIs throughout our 19+ years of experience. In this article, we share the fundamentals of the API world with you.

What Is REST?

REST (Representational State Transfer) is an architectural style defined by Roy Fielding in 2000. RESTful APIs aim to create simple, scalable, and reliable services using the existing web infrastructure.

The core principles of REST are:

• Client-Server separation: Client and server can be developed independently
• Statelessness: Each request must contain all the information needed to be processed
• Cacheability: Responses can be marked as cacheable
• Layered system: The client cannot tell whether it's connected directly to the server or an intermediary
• Uniform interface: Resources must be accessible in a consistent manner

HTTP Methods

In RESTful APIs, the appropriate HTTP method is used for each operation:

• GET: Read resources (fetch data)
• POST: Create new resources
• PUT: Fully update existing resources
• PATCH: Partially update existing resources
• DELETE: Delete resources

Proper use of these methods ensures your API is understandable and consistent.

Endpoint Design Principles

Good endpoint design directly affects the usability of your API. Here are the golden rules:

• Naming: Use nouns, not verbs → /users is correct, /getUsers is wrong
• Plural form: Collection names should be plural → /products, /orders
• Hierarchy: Show related resources in a nested structure → /users/123/orders
• Filtering: Use query parameters → /products?category=electronics&sort=price
• Versioning: Specify the API version in the URL → /api/v1/users
• Consistency: Apply the same naming convention across all endpoints

HTTP Status Codes

Using correct status codes improves the communication quality of your API:

• 200 OK: Successful request
• 201 Created: New resource created
• 204 No Content: Successful but no content to return
• 400 Bad Request: Invalid request
• 401 Unauthorized: Authentication required
• 403 Forbidden: Insufficient authorization
• 404 Not Found: Resource not found
• 500 Internal Server Error: Server error

API Security

API security is one of the most critical topics in modern software development:

Authentication and Authorization

• JWT (JSON Web Token): The most common method for stateless authentication
• OAuth 2.0: Standard protocol for third-party access authorization
• API Key: Can be used for simple projects but is not sufficient on its own

Security Best Practices

• HTTPS requirement: Encrypt all API traffic
• Rate limiting: Restrict excessive request submissions
• Input validation: Validate all incoming data
• CORS policy: Allow access only from permitted origins
• Sensitive data masking: Hide personal information in logs

API Documentation

A good API is complemented by good documentation. Using the Swagger/OpenAPI standard:

• Document all your endpoints interactively
• Add sample requests and responses
• List error codes and their descriptions
• Describe the authentication process in detail

Conclusion

RESTful API design is one of the fundamental building blocks of modern software architecture. An API designed with the right principles improves both the developer experience and system reliability.

At BUZ Yazılım, we develop secure, performant, and scalable API solutions for over 100 of our clients' projects. If you need support with API design or integration, contact us.