HTTP Status Codes Reference

Complete HTTP status codes reference — every code from 1xx to 5xx explained in plain English, with SEO impact notes.

HTTP status codes (also called HTTP response codes or HTTP error codes) are three-digit numbers returned by a server to describe the outcome of a request. Select a code below for a full explanation and its SEO impact.

2xx Success

200 OK The request succeeded and the server returned the requested resource. 201 Created The request succeeded and a new resource was created (typically after POST requests). 204 No Content The request succeeded but there is no content to return.

3xx Redirection

301 Moved Permanently The resource has been permanently moved to a new URL. Browsers and crawlers should update their references. 302 Found (Temporary Redirect) The resource is temporarily available at a different URL. The original URL should still be used for future requests. 304 Not Modified The resource has not changed since the last request. The browser can use its cached version. 307 Temporary Redirect Like 302, but the request method must not change. 308 Permanent Redirect Like 301, but the request method must not change.

4xx Client Errors

400 Bad Request The server cannot process the request due to malformed syntax. 401 Unauthorized Authentication is required and has not been provided or has failed. 403 Forbidden The server understood the request but refuses to authorize it. 404 Not Found The requested resource could not be found on the server. 410 Gone The resource has been permanently removed and will not return. 429 Too Many Requests The user has sent too many requests in a given timeframe.

5xx Server Errors

500 Internal Server Error A generic server error. The server encountered an unexpected condition. 502 Bad Gateway The server received an invalid response from an upstream server. 503 Service Unavailable The server is temporarily unable to handle requests, often because it is overloaded or under maintenance. 504 Gateway Timeout The server did not receive a timely response from an upstream server.

HTTP status code families

HTTP status codes are grouped into five classes by their first digit.

1xx Informational — the request was received and processing is continuing.
2xx Successful — the request was received, understood, and accepted.
3xx Redirection — further action is needed to complete the request.
4xx Client errors — the request contains bad syntax or cannot be fulfilled. These are errors on the client side.
5xx Server errors — the server failed to fulfil a valid request. These are errors on the server side.

SEO impact of HTTP response codes

Search engines follow redirects and eventually update their index to reflect the destination URL. A 301 (permanent redirect) passes most link equity to the destination; a 302 (temporary redirect) may not. Pages returning 404 or 410 are typically removed from the index. Pages returning 5xx server errors may be temporarily de-ranked if the errors persist across many crawls.

Frequently asked questions

What is a 400 error?

A 400 Bad Request error means the server could not process the request because of malformed syntax on the client side. Common causes include invalid JSON in a request body, missing required parameters, an incorrect Content-Type header, or a URL that is too long.

What is a 500 error?

A 500 Internal Server Error is a generic server-side error meaning something went wrong on the server but it cannot be more specific. Common causes include unhandled exceptions in application code, misconfigured server environments, or a database connection failure.

What is a 404 error?

A 404 Not Found error means the server could not find the requested resource at that URL. The page may have been deleted, moved without a redirect, or the URL may simply be wrong. Google removes persistent 404 pages from its index and they waste crawl budget.

What is the difference between 401 and 403?

401 Unauthorized means the request lacks valid authentication credentials — the user is not logged in or the token is expired. 403 Forbidden means the server understood who the user is but they do not have permission to access that resource.

What does a 302 redirect mean?

A 302 Found redirect is a temporary redirect — the resource is currently at a different URL but the original URL should still be used in future. Use 301 Moved Permanently when the move is final, so search engines update the indexed URL and pass link equity to the new location.

What are 5xx server errors?

5xx status codes indicate that the server failed to fulfil a valid request — the problem is on the server side, not the client's. Common 5xx errors: 500 Internal Server Error, 502 Bad Gateway, 503 Service Unavailable, 504 Gateway Timeout.