HTTP status codes: the numbers behind the web

Published July 7, 2026 · By NumberWiki

Every time you open a web page, your browser and the server hold a short conversation, and the server's first word back is always a number. These three-digit HTTP status codes tell the browser what happened: whether the page was found, moved, forbidden, or broken. You've met 404; here's the rest of the family, and what each number is really saying.

The five classes

Status codes are grouped by their first digit, which tells you the general outcome at a glance:

1xx — Informational: "Got it, keep going."
2xx — Success: "Here's what you asked for."
3xx — Redirection: "What you want is somewhere else."
4xx — Client error: "You made a mistake."
5xx — Server error: "I made a mistake."

200 OK, and the success family

200 OK is the code you never see, because it means everything worked — the silent success behind the vast majority of the web. Its relatives fill in the details: 201 Created after you successfully submit something new, 204 No Content when a request succeeds but there's nothing to send back, and 206 Partial Content, the code that makes it possible to resume a paused download or scrub to the middle of a video.

301 vs 302: the two kinds of redirect

Redirects are how the web reorganises itself without breaking links. The distinction between the two common ones matters enormously for search engines. 301 Moved Permanently says "this page has moved for good, update your bookmarks" — search engines transfer the old page's ranking to the new address. 302 Found (confusingly named) means "temporarily somewhere else, but keep asking here." Using the wrong one is a classic SEO mistake.

404, and the famous 4xx errors

404 Not Found is the most famous number on the internet — so recognisable that custom 404 pages have become an art form. It means the server is fine but the specific page doesn't exist. Its siblings are worth knowing: 400 Bad Request (the browser sent something malformed), 401 Unauthorized (you need to log in), 403 Forbidden (you're logged in but not allowed), 429 Too Many Requests (slow down — you're being rate-limited), and the poetic 451 Unavailable For Legal Reasons, whose number is a deliberate nod to Ray Bradbury's Fahrenheit 451, the temperature at which books burn.

418 I'm a teapot

The internet's best in-joke lives at 418 I'm a teapot. It comes from the Hyper Text Coffee Pot Control Protocol, an April Fools' Day specification published in 1998, in which a teapot asked to brew coffee responds "I'm a teapot." It was never meant to be real — yet it's so beloved that it survives in web frameworks and real APIs to this day, and attempts to remove it from the standards have been beaten back by popular demand.

500 and the server errors

When the number starts with a 5, the problem is on the server's end. 500 Internal Server Error is the generic "something broke and we don't want to say what" code. 502 Bad Gateway and 504 Gateway Timeout appear when servers talking to other servers get no answer, and 503 Service Unavailable is what you get when a site is overloaded or down for maintenance — the code behind many a "we'll be right back" page.

Why three digits?

The scheme dates to the earliest days of HTTP in the early 1990s, and it was designed to be read by machines first and humans second: a program only needs to check the first digit to know whether to celebrate, follow a redirect, or raise an error, while the full number carries the specifics. That simple idea has scaled from a handful of codes to dozens, and it's why the same numbers you see in a browser error also show up in server logs, API responses, and developer consoles the world over.

On NumberWiki

Any number that is a registered HTTP status code shows an "HTTP status" note on its page. Try 200, 301, 404, 418, 451, or 500 to see each one in context — several of them, like 451 and 8080, carry more than one meaning across the different domains the site decodes.