API Testing Complete Notes — Beginner to Advanced

Overview

This handbook provides comprehensive API testing notes, progressing from beginner to advanced topics. It covers foundational concepts like HTTP, REST, and JSON, and expands into advanced areas such as authentication, contract testing, security, performance, CI/CD, and debugging. The content is aligned with RFC 9110 HTTP semantics and current OpenAPI guidance, specifically OpenAPI 3.2.1. Designed for QA Engineers, Testers, and SDETs, the notes start with API fundamentals and build into validation, automation, and integration. Each page presents one concept with a practical example, tester verification points, and common mistakes to avoid. Users new to API testing can read sequentially, while experienced testers can focus on specific advanced sections.

Table of contents

1. What Is an API?
2. Why API Testing Is Important
3. Client-Server Model
4. HTTP Request Anatomy
5. HTTP Response Anatomy
6. URL Anatomy
7. HTTP Methods Overview
8. Safe and Idempotent Methods
9. GET Testing
10. POST Testing
11. PUT Testing
12. PATCH Testing
13. DELETE Testing
14. Status Code Families
15. Common 2xx Status Codes

Who this resource is for

• API Tester
• QA Engineer