Wirebook › Lesson 5 of 18
What do 404 and friends mean?
Every answer a website sends starts with a three-digit number. You normally never see it, except when things go wrong, like the famous 404. Learn to read them and you can tell whose fault a problem is.
The ones worth knowing
200 OK- Everything worked.
301 Moved Permanently- The page has a new address for good; search engines update their records.
304 Not Modified- "You already have the latest copy", so nothing needs downloading. A big speed trick.
403 Forbidden- The server knows what you want and says no.
404 Not Found- Nothing lives at that address. Often a typo or an old link.
405 Method Not Allowed- You can look but not touch: e.g. trying to send data to a read-only page.
418 I'm a teapot- An April Fools' joke from 1998 that people loved so much it stuck around.
429 Too Many Requests- Slow down! A rate limit protecting the server (see Can a website get tired?).
500 Internal Server Error- Something crashed inside the server.
Grown-up twin: look up any code with Anvil’s free HTTP status API (GET /v1/http-status/404) — plain words, related codes and retry advice. Deeper help pages: Tooltern’s 401 vs 403, 429, 502, 503 and 504.