What is an API

What is an API

This lesson covers What is an API as part of REST API Masterclass – From Zero to Professional PHP API. Focus is PHP 8 REST API implementation with JSON responses, correct HTTP status codes, and structure suitable for mobile and web clients.

Module «Introduction to API and HTTP» builds practical skills step by step from theory to router, controllers, JWT auth, and deployment. Each example uses employee/users domain as reference — aligned with the final employee management system project.

In depth

We explain What is an API in depth: endpoint design, HTTP methods and status codes, JSON body and error formatting. In PHP use ResponseHelper and ErrorHandler classes for consistent responses. Test with curl and Postman before releasing changes to staging.

Key points

• Understand the concept: What is an API in REST API context.
• Map HTTP method, status code, and JSON envelope to the business case.
• Implement in PHP 8 with separate router, controller, and model layers.
• Test endpoints with curl or Postman collections before production.
• Document expected input, output, and errors in OpenAPI specification.
• Security review: authentication, validation, and rate limiting where needed.
• Measure performance and log requests for production maintenance.

Practical example

Example GET call to a REST API

curl -i https://api.example.com/v1/users
        # HTTP/1.1 200 OK
        # Content-Type: application/json
        # {"data":[{"id":1,"email":"ana@firma.rs"}]}

Common mistake

Common mistakes with What is an API: mixing GET/POST semantics, returning HTML instead of JSON, wrong status codes (e.g. 200 instead of 404), or exposing SQL/stack traces. In production always use HTTPS, input validation, and centralized error handling.

Summary

After this lesson you understand What is an API and can apply it in your PHP REST API project. Practice on a local api/ folder with index.php router and document the endpoint in OpenAPI before the next lesson in module 1.