How HTTP Status Codes Work

Every time your browser asks a web server for something, the server answers with a three-digit status code that summarizes the outcome: did it find the page, did it move, was it forbidden, or did it break? Knowing what the codes mean turns a confusing error page into a useful diagnosis. The HTTP Status Checker shows you the real code, the redirect chain and the response headers for any URL; this guide explains how to read what it returns.

The five code groups

Status codes are grouped by the first digit:

1xx — Informational

Rarely visible to you. The server is saying “I got your request and I’m continuing.” Examples: 100 Continue, 101 Switching Protocols (used to start WebSocket connections).

2xx — Success

The request worked. 200 OK is the ordinary success you see for almost every normal page load. 201 Created appears after creating a resource; 204 No Content when everything is fine but there is nothing to return. If your URL returns 200 and the page looks right in a browser, this is the healthy case.

3xx — Redirection

The browser is being sent somewhere else. Codes you will actually meet:

• 301 Moved Permanently — the page has moved for good; search engines transfer most of its signals to the new URL.
• 302 Found — a temporary redirect, often used after form submissions or by login flows.
• 307 / 308 — like 302/301 but preserving the request method (POST stays POST).
• 304 Not Modified — the browser’s cached copy is still valid; no full download needed.

A chain of several redirects (for example http:// → https:// → www → with a trailing-slash fix) is functionally fine but adds a round trip per hop. If the chain never ends in a 2xx, you have a redirect loop — a real problem that makes the page unreachable.

4xx — Client errors

The request, as sent, can’t be fulfilled. The most famous is 404 Not Found: the URL does not exist on that server. Others: 403 Forbidden (exists, but access denied), 401 Unauthorized (login required), 429 Too Many Requests (rate-limited). A 404 for a genuinely removed page is honest and normal; a 404 for a page your menu links to is a bug worth fixing.

5xx — Server errors

The server got the request but failed while handling it. 500 Internal Server Error is the generic version; 502 Bad Gateway and 504 Gateway Timeout usually mean a proxy (such as a CDN or load balancer) could not reach or wait for the backend. These are always worth investigating — visitors who hit a 5xx frequently give up.

Read the chain, not just the final code

A checker that only says “200 OK” hides useful information. The full redirect chain tells you whether your site wastes round trips, whether the canonical URL is what you expect, and whether HTTPS is the final destination. In the HTTP Status Checker, start at the URL you entered and follow every hop until a final 2xx (or a terminal error).

Status codes and SEO

From a search perspective the interesting ones are 3xx and 4xx:

• Permanent moves should use 301 so signal moves with the page; using 302 for a permanent move leaks that signal over time.
• Old URLs returning thousands of 404s is rarely a crisis by itself — but important pages returning 404 by mistake, or internal links pointing into 404s, are problems.
• The canonical URL guide covers the related question of duplicates vs. redirects.

Why two tools can disagree

Requests come from different servers in different countries at different moments, so caching, geo-routing or a CDN rule can legitimately cause two checkers to return different codes for the same URL. When they disagree, verify with a private browsing window from your own network and compare the chain in both results.