Start from our web crawling and data collection basics guide if you’re new
In our previous articles on the origins of the HTTP protocol, HTTP request methods, and how HTTP proxies work, we laid the foundation for understanding how the web communicates.
In this article, we focus on another critical piece of that communication layer: HTTP status codes and their practical meaning in real-world systems.
If you browse the web regularly, you have almost certainly encountered the famous 404 error. It appears when a link is broken and has become so iconic that it is now part of internet culture. Behind that short message lies a structured signaling system that every web application relies on.
What Are HTTP Status Codes?
The HTTP protocol defines how clients and servers communicate. If HTTP methods such as GET and POST act as the verbs of this language, then HTTP status codes function as its signals.
Each status code is a three-digit number returned by the server to describe the result of a request. Instead of long explanations, the server sends a compact code that conveys meaning instantly—much like shorthand signals in human communication.
For example:
- 200 means “Success, here is your content”
- 404 means “The requested resource does not exist”
- 500 means “Something went wrong on the server”
Originally defined in RFC 2616, HTTP status codes were later extended through standards such as RFC 2518, RFC 2817, RFC 2295, RFC 2774, and RFC 4918.
You can review the official specifications via the IETF RFC Index.
The HTTP Status Code Family Tree
All HTTP status codes fall into five categories based on their first digit. This structure allows developers and clients to immediately understand the nature of a response.
1xx – Informational Responses
These codes indicate that the server has received the request and is continuing to process it.
Common examples include:
- 100 Continue – The server has received the request headers and is ready for the body (useful for large POST requests).
- 101 Switching Protocols – The server agrees to change protocols, commonly seen when upgrading to WebSocket.
Although rarely handled explicitly in application code, these responses are essential for protocol-level optimizations.
2xx – Successful Responses
This category signals that the request was successfully received, understood, and processed.
Typical HTTP status codes in this range include:
- 200 OK – Standard success response.
- 201 Created – A new resource was successfully created, often used after registration or object creation.
- 204 No Content – The request succeeded, but there is no response body.
- 206 Partial Content – Partial data returned, commonly used for resumable downloads.
3xx – Redirection Responses
Redirection codes indicate that the client must take additional action to complete the request.
Common examples are:
- 301 Moved Permanently – The resource has a new permanent URL and may be cached by browsers.
- 302 Found – A temporary redirect, frequently used during login flows.
- 304 Not Modified – The cached version remains valid, improving performance and reducing bandwidth.
Correct use of these HTTP status codes significantly improves caching efficiency and SEO behavior.
4xx – Client Error Responses
4xx responses mean that the request contains an error caused by the client.
Important examples include:
- 400 Bad Request – The request is malformed or invalid.
- 401 Unauthorized – Authentication is required but missing.
- 403 Forbidden – The user is authenticated but lacks permission.
- 404 Not Found – The requested resource does not exist.
- 405 Method Not Allowed – The HTTP method is not supported for this endpoint.
Distinguishing between these codes helps developers diagnose issues quickly and improves API usability.
5xx – Server Error Responses
When the server fails to process a valid request, it returns a 5xx response.
Common server-side errors include:
- 500 Internal Server Error – A generic server failure.
- 502 Bad Gateway – A proxy received an invalid response from an upstream server.
- 503 Service Unavailable – The server is overloaded or under maintenance.
- 504 Gateway Timeout – The upstream server did not respond in time.
In distributed systems and proxy-based architectures, these HTTP status codes are critical for monitoring and alerting.
Best Practices for Using HTTP Status Codes
Using HTTP status codes correctly makes APIs clearer, more predictable, and easier to integrate.
Recommended best practices include:
- Return 201 Created instead of 200 OK when a resource is newly created.
- Use 404 Not Found rather than 500 Internal Server Error for missing resources.
- Provide descriptive error details alongside 400 Bad Request responses.
- Clearly distinguish 401 Unauthorized (not logged in) from 403 Forbidden (no permission).
These distinctions are especially important in web scraping and proxy systems, where large-scale request handling depends on accurate response signaling.
For example, proxy infrastructures processing hundreds of thousands of requests per day rely on HTTP status codes to detect retries, failures, and access restrictions efficiently.
Conclusion
HTTP status codes are far more than simple error numbers. They form a compact yet powerful communication system between clients and servers, enabling efficiency, clarity, and scalability across the web.
By understanding and using HTTP status codes correctly, developers can build more reliable APIs, improve debugging efficiency, and design systems that behave predictably under real-world conditions.
In upcoming articles, we will continue exploring advanced HTTP topics, including caching strategies, retry mechanisms, and proxy-based architectures.