REST API — HTTP Status Codes

🌐 HTTP / RFC 9110 🟢 Chapter 4 of 39 📂 Phase 02: HTTP Fundamentals 📅 2026 Edition

📌 Covered in this chapter: 1xx informational · 2xx success · 3xx redirection · 4xx client errors · 5xx server errors · 200 OK · 201 Created · 202 Accepted · 204 No Content · 400 Bad Request · 401 Unauthorized · 403 Forbidden · 404 Not Found · 409 Conflict · 422 Unprocessable Content · 429 Too Many Requests · 500 Internal Server Error · 503 Service Unavailable

Welcome to REST API — HTTP Status Codes in our REST API Complete Masterclass! HTTP status codes five major classes lo grouped untayi; 4xx client errors, 5xx server errors indicate chestayi.

1Simple Introduction

In web application engineering, understanding HTTP Status Codes is essential for building scalable, secure, and developer-friendly REST APIs. REST APIs communicate using HTTP protocol standards and JSON representations.

2What You Will Learn

📚 Learning Objectives:

Master HTTP protocol mechanics behind HTTP Status Codes
Understand request/response semantics, headers, and status code specifications
Design standardized, production-ready RESTful endpoints and JSON payloads
Avoid common architectural pitfalls, security flaws, and breaking API changes

3Why HTTP Status Codes is Useful

💡 Practical Utility

REST APIs connect web frontends, mobile applications, microservices, and third-party integrations. Mastering HTTP Status Codes equips developers to build robust API backends in Node.js, Python, Java, Go, Ruby, and PHP.

4Resource Design

Target Resource Entity: courses. RESTful resource design focuses on nouns representing business domain objects rather than action verbs.

5HTTP Method

HTTP Method: GET. Defines the operation performed on the target resource contract.

6Endpoint URL

Target Endpoint URL

GET /api/v1/courses/999

7Request Example

HTTP Request Example

GET /api/v1/courses/999 HTTP/1.1

8Response Example

HTTP Response Example

404 Not Found
{
  "error": {
    "code": "COURSE_NOT_FOUND",
    "message": "Requested course ID 999 does not exist"
  }
}

9Status Code

HTTP Status Code: 404 Not Found

Indicates successful execution or specific client/server error condition per RFC 9110 semantics.

10Server-Side Flow

HTTP Request Received -> Router Matching -> Authentication & CORS -> Validation -> Service Logic -> Database Operation -> JSON Serialization -> HTTP Response

11Validation

Server-side request validation ensures required fields, data types, email formats, and parameter ranges are satisfied before executing database queries. If validation fails, the API responds with 422 Unprocessable Content.

12Database Operation

Queries are executed using parameterized SQL or ORM abstractions (e.g. SELECT, INSERT, UPDATE, DELETE), preventing SQL injection vulnerabilities.

13Common Mistakes

⚠️ Anti-Patterns to Avoid

Using verbs in URLs (e.g. /getCourses or /createCourse).
Returning 200 OK for all error responses containing {"error": true} inside JSON.
Failing to validate input or concatenating unescaped SQL/NoSQL query strings.
Confusing Authentication (who you are) with Authorization (what you can do).
Returning huge dataset lists without pagination.
Hardcoding API secrets or credentials in public client code.

14Coding Challenge

🎯 Hands-On Challenge:

Create a REST API for lessons featuring: GET /api/v1/lessons, GET /api/v1/lessons/{id}, POST /api/v1/lessons, PATCH /api/v1/lessons/{id}, DELETE /api/v1/lessons/{id} with request validation, pagination, search, authentication, error response envelopes, and OpenAPI documentation!

15Mini Quiz

❓ Question: What is the primary role of HTTP Status Codes in REST API design?

Answer: It provides standardized HTTP mechanisms for 1xx informational, building predictable and scalable APIs.

16Quick Recap

HTTP status codes five major classes lo grouped untayi; 4xx client errors, 5xx server errors indicate chestayi.
POST creates resources (201 Created), GET reads data (200 OK), PATCH partially updates (200 OK), DELETE removes resources (204 No Content).
Follow RFC 9110 HTTP semantics, status code standards, and REST design best practices.

Written by Our Compiler Technical Editorial Team
Reviewed for accuracy & tested on RFC 9110 HTTP Standards · Last updated August 2026