Introduction
When you browse the web or build an API, every request you send receives a response and that response includes an HTTP status code. These codes are like tiny signals that tell you what happened behind the scenes: whether the request was successful, redirected, or failed due to an error.
In this post, we’ll break down the most common HTTP response codes, explain what each category means, and share how developers can use them effectively when building web applications and APIs.
What Are HTTP Response Codes?
HTTP (HyperText Transfer Protocol) response codes are three-digit numbers returned by a web server in response to a client’s request (like when your browser loads a page or your app calls an API).
Each code helps both browsers and developers understand the result of that request — success, redirection, client error, or server error.
The 5 Categories of HTTP Status Codes
1xx – Informational Responses
These indicate that the request has been received and is still being processed.
- 100 Continue: The server received the request headers and the client can continue sending the body.
- 101 Switching Protocols: The server is switching to a different protocol as requested by the client.
Rare in typical web apps, but useful in advanced scenarios like protocol switching (e.g., upgrading to WebSockets).
2xx – Success Responses
These codes mean the request was successfully received, understood, and processed.
- 200 OK: The standard success response for most HTTP requests.
- 201 Created: A new resource has been successfully created (commonly used in POST requests).
- 204 No Content: The server successfully processed the request but didn’t need to return data.
Always use specific success codes like 201 or 204 to make your APIs more meaningful.
3xx – Redirection Responses
The client must take additional action to complete the request.
- 301 Moved Permanently: The resource has a new permanent URL.
- 302 Found: Temporary redirect.
- 304 Not Modified: Used for caching — tells the browser that the resource hasn’t changed since the last request.
Useful for SEO redirects or when optimizing page caching for performance.
4xx – Client Error Responses
These indicate that the problem came from the client’s side (like a bad request or unauthorized access).
- 400 Bad Request: The server can’t understand the request due to invalid syntax.
- 401 Unauthorized: Authentication is required.
- 403 Forbidden: The user doesn’t have permission to access the resource.
- 404 Not Found: The resource doesn’t exist.
- 429 Too Many Requests: The user has sent too many requests in a short period (rate limiting).
Always provide user-friendly error messages for 4xx responses in your applications.
5xx – Server Error Responses
These indicate that the error came from the server’s side.
- 500 Internal Server Error: A generic error message for unexpected failures.
- 502 Bad Gateway: The server received an invalid response from an upstream server.
- 503 Service Unavailable: The server is temporarily overloaded or under maintenance.
- 504 Gateway Timeout: The server didn’t receive a timely response from another service.
Always log 5xx errors in your backend to help identify issues early.
Why HTTP Status Codes Matter for Developers
- Debug API and network errors faster.
- Improve SEO by handling redirects and errors correctly.
- Provide meaningful responses to users and clients.
- Build more reliable and secure applications.
Conclusion
HTTP response codes are the universal language of the web. Once you understand what they mean, debugging becomes easier, performance improves, and user experience gets smoother.
Next time you see a 404, 500, or 200, you’ll know exactly what’s happening behind the curtain.
