Every time you visit a website, your browser and the server have a little chat. Sometimes, that conversation goes smoothly; sometimes, there’s a misunderstanding, and sometimes, everything falls apart. HTTP response codes communicate success, confusion, or complete failure.
If you’ve ever seen a dreaded 404 Not Found or a mysterious 500 Internal Server Error, you’ve already encountered them. But what do these numbers actually mean, and why should you care? Let’s break it down.
The Five Families of HTTP Status Codes
HTTP response codes are grouped into five categories, each with its own purpose. Think of them as different types of replies in a conversation.
1xx: Informational – “Hang Tight, Something’s Happening”
These codes are rarely seen in everyday browsing because they’re primarily for behind-the-scenes communication between client and server. They indicate that a request has been received and is being processed.
- 100 Continue – The server says, “Got your request, keep going.”
- 101 Switching Protocols – “We’re changing things up. Let’s upgrade to a new protocol.”
2xx: Success – “All Good!”
This is the best category. Everything went according to plan, and the server successfully handled the request.
- 200 OK – The gold standard of success. Everything worked, and here’s your requested data.
- 201 Created – Used when a new resource has been created (like when you sign up for a new account).
- 204 No Content – “Request processed, but there’s nothing to return. Move along.”
3xx: Redirection – “You Need to Go Over There”
Redirection codes mean the resource you’re looking for isn’t exactly where you thought it was, but don’t worry—the server is pointing you in the right direction.
- 301 Moved Permanently – “This page has moved. Update your bookmarks.”
- 302 Found – “The resource is somewhere else, but only for now.”
- 304 Not Modified – “You already have the latest version, so there is no need to download it again.” or “What you are trying to modify is not different from what you sent.”
4xx: Client Errors – “You Messed Up”
These errors happen when the client (browser, app, user) makes a mistake. They usually mean the request was invalid or unauthorized.
- 400 Bad Request – “Something’s wrong with your request. Check your syntax.”
- 401 Unauthorized – “You need to log in before accessing this.”
- 403 Forbidden – “Even if you log in, you don’t have permission.”
- 404 Not Found – “Whatever you’re looking for isn’t here. Maybe it never was.”
5xx: Server Errors – “We Messed Up”
This is when the problem is on the server’s end, and there’s nothing the client can do about it.
- 500 Internal Server Error – “Something broke on our end. Try again later.”
- 502 Bad Gateway – “We asked another server for help, but it didn’t respond correctly.”
- 503 Service Unavailable – “The server is too busy or down for maintenance.”
Common HTTP Status Codes in the Wild
Some codes appear way more often than others. Here are the usual suspects:
- 200 OK – Everything is fine.
- 404 Not Found – The page doesn’t exist. Maybe it used to, maybe it never did.
- 500 Internal Server Error – Something went wrong, but the server won’t tell you what.
Using HTTP Status Codes Correctly
Understanding HTTP response codes is great, but using them correctly in applications is even more important. Here’s how they should map to application logic:
- Returning 200 OK for everything? Bad idea. Return a 404, not a generic 200 if something isn’t found.
- Use 201 Created when making new resources. If a user submits a form to create a new post, the API should return 201 Created instead of 200 OK.
- When nothing is returned in the response body, you should use 204 No Content for success. This will not only save on return size but also tell the client an important message.
- I like to return 304 Not Modified when the backend system does not change the state of a resource. This is a great message when saving something identical to what is in your database or filesystem.
- Handle 429 Too Many Requests when rate limiting. If a user or bot is hitting your API too fast, don’t just block them—return 429 Too Many Requests with a message about rate limits.
- 500s should be logged, not ignored. If your app returns a 500 Internal Server Error, it’s a sign that something’s wrong on the backend. Make sure errors are logged so they can be fixed.
Conclusion
HTTP response codes are the web’s way of communicating what’s happening. Whether you’re a developer troubleshooting an issue, an API designer structuring your endpoints, or just someone trying to understand why a webpage isn’t loading, knowing these codes can make your life much easier. So next time you see a 404 Not Found, you’ll know exactly what’s happening.