HTTP status codes explained for visitors: 403, 404, 500, 502 and 503

How to read a status code

The codes are defined in RFC 9110, the HTTP standard, and MDN keeps a readable list of every one. The first digit tells you the family of the answer. Codes starting with 2 mean success, 3 means the page is somewhere else, 4 means the server rejected the request as it was sent, and 5 means the server itself failed. That first digit alone is often enough to tell whether you should wait for the site to recover or change something on your side.

The checker on the homepage shows the status code of the final answer, after following any redirects. It is often the clearest single clue about what kind of problem you are looking at.

The codes you are most likely to see

What to do with 4xx codes

Codes in the 400 range say the request was not acceptable as sent. That sometimes means you should change something, and sometimes means the site is deliberately keeping certain visitors out.

1. Check the address

   A typo or an outdated link causes most 404 errors.

2. Turn off the VPN or proxy

   Many 403 errors come from sites that block known VPN addresses.

3. Sign in

   A 401 or a 403 on a members’ page often just means the session expired.

4. Slow down

   A 429 means too many requests; wait a few minutes before reloading.

5. Try another network

   Some 403 errors are regional or network-wide blocks.

What to do with 5xx codes

Codes in the 500 range mean the site failed to answer properly. There is nothing to fix on your side. Waiting a few minutes and checking again is the right response. During large incidents, 502, 503 and 504 errors often alternate as servers restart and traffic shifts between them. Avoid repeating payments or form submissions while these errors appear, because the first attempt may have gone through before the error was shown.

Redirects and why they matter

Many sites answer the first request with a redirect: from http to https, from the bare domain to www, or to a country or login page. One or two redirects are normal. A long chain or a loop that never ends is not, and browsers give up after a limit. The checker lists every redirect it followed so you can see where a request finally ended and whether the chain looks healthy.

When the status code is not the whole story

A status code describes one answer to one request. A page can return 200 and still fail later when it loads scripts, images or data from other servers. Apps can fail even when the website answers normally, because they talk to different servers. Treat the status code as a strong first clue, then use the response time, the redirects and the other guides to complete the picture.

Rarer codes that still turn up

A few codes outside the usual handful are worth recognizing, because each one closes a question quickly.

401 Unauthorized sounds like 403 but means something narrower: the server wants credentials and did not get valid ones. Signing in, or signing in again after a password change, is the fix. A 403 can persist after a perfect login. A 401 normally does not.

410 Gone is the honest cousin of 404. The site is telling you that the page existed and was removed on purpose, with no forwarding address. Retrying will not help, and neither will waiting. Search the rest of the site for a replacement.

451 Unavailable For Legal Reasons is rare but unmistakable. It was added to HTTP in 2016 through RFC 7725, and its number is a nod to Ray Bradbury’s Fahrenheit 451. A site sends it when a court order or a regulation keeps it from showing the page in your country. Nothing is broken; the block is deliberate and tied to location.

304 Not Modified belongs to a different conversation entirely. It tells your browser that its stored copy is still current, so the page loads from cache. You will see it in developer tools, never as an error page.

No code at all

Sometimes there is no status code to read, because the server never replied. Timeouts, refused connections and name lookups that fail happen before HTTP even starts, and browsers show their own error pages for them instead of anything from the site. The tutorial on browser connection errors and how to work through them starts exactly where this guide ends, with those messages and the order in which to test them.

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