Whenever a server can’t successfully process an HTTP request, it responds with an HTTP status code—404, 403, 503, and so on. You’ve probably seen them all before, and they’re rarely more than a minor annoyance. But what do these codes actually mean, and why are they sent in the first place? You’ll find the answers here.
In this article
With technical SEO more Leads
Every time a website, webpage, or homepage is loaded, a client—such as a browser—and the requested web server communicate with each other. This creates a question-and-answer process. In essence, the client and server exchange information about how well (or poorly) a specific request was handled. Data transfer happens through the Hypertext Transfer Protocol (HTTP). After the client sends a request, the server responds with an HTTP status code in the form of a three-digit number. This tells the browser (client) whether the request was successful, whether an error occurred, or whether authentication is required. The resulting status is automatically embedded in the header of every HTTP response.
Users typically only notice these status codes when the server fails to respond to the client’s request or when the protocol can’t be executed or permitted. In those cases, the status code appears to internet users in the form of an automatically generated HTML page—essentially, only when no web data can be delivered.
The ABCs of HTTP Status Codes
Based on the URL structure, the browser sends a request to a specific server where the website should theoretically be located. The server then attempts to deliver the requested data to the client—usually successfully, but sometimes not. Depending on the outcome, the server responds with a code. This response message is what we call an HTTP status code, and it’s defined by the Hypertext Transfer Protocol (HTTP).
How and Why HTTP Status Codes Are Classified
HTTP status codes are always three digits long and fall into five distinct classes. This classification isn’t arbitrary—it’s based on the function and meaning of the codes. The Internet Assigned Numbers Authority (IANA) maintains the official registry of HTTP status codes.
- The first digit indicates the class (e.g., 404 belongs to the 4xx class).
- The last two digits don’t have categorizing functions; they just specify the exact code.
The five classes are:
- 1xx – Informational: The request has been received and processing continues. These codes provide updates during the request.
- 2xx – Success: The request was successfully received, understood, and accepted.
- 3xx – Redirection: Additional action is needed to complete the request. Often used for redirects.
- 4xx – Client Error: The request is invalid or cannot be fulfilled. Usually caused by a client-side issue.
- 5xx – Server Error: The server failed to fulfill a valid request. Usually a temporary server-side problem.
For 4xx and 5xx errors, servers typically generate automatic HTML error pages so users can see what went wrong.
Your website, always up to date
The Most Important and Common HTTP Status Codes
- 200 – OK: The requested resource was found and delivered to the client.
- 301 – Moved Permanently: The resource has been permanently moved. The new location is provided so the client can redirect. This is the standard permanent redirect.
- 302 – Found (Moved Temporarily): The resource is temporarily located elsewhere, but the original URL remains valid. Users and search engines often prefer 301s over 302s for consistency.
- 400 – Bad Request: The server cannot process the request due to a client error (e.g., malformed syntax, invalid framing). Often fixed by retyping the URL or clearing cache and cookies.
- 403 – Forbidden: The request was understood, but the server refuses to fulfill it. This usually means the user lacks proper authorization or an account is required.
- 404 – Not Found: The classic error. The resource doesn’t exist at the specified URL. Links pointing to such pages are known as “dead links.”
- 503 – Service Unavailable: The server is temporarily overloaded or undergoing maintenance. Usually a short-term issue that resolves quickly.
SEO Impact of HTTP Status Codes
Googlebot crawls websites at regular intervals. To maintain visibility in search results, all linked content and URLs need to be accessible. Content that repeatedly returns errors or is unreachable will eventually be dropped from the Google index—and disappear from search results.
We boost your digital visibility!
Conclusion
Out of all the valid HTTP status codes, most everyday internet users are familiar with only a handful—most notably the infamous 404 Not Found. The majority of status codes, however, exist purely for communication between client and server. Still, when it comes to SEO, administrators should consistently monitor these status messages and be ready to fix issues whenever necessary.
FAQ: HTTP Statuscodes
What are HTTP status codes?
What classes of HTTP status codes are there?
- 1xx (Informational): Request is still in progress, more info to follow
- 2xx (Success): Everything worked (e.g., 200 OK)
- 3xx (Redirection): The resource has moved (e.g., 301 Redirect)
- 4xx (Client Error): Request is faulty (e.g., 404 Not Found)
- 5xx (Server Error): Server can’t process the request (e.g., 503 Unavailable)
What does HTTP status code 404 mean?
A 404 “Not Found” means the requested page doesn’t (or no longer) exists. Common causes include dead links or deleted content. For users, it’s frustrating—and for SEO, it can mean losing valuable rankings.
