Status codes · one code404 — Not Found
What a 404 Not Found response means, who is at fault, what a visitor should do and what the server owner should do.
Open the reference on this codeWhat to do
If it is someone else's site
Check the address character by character: a stray trailing slash, a Cyrillic letter in place of a Latin one, a link broken across lines in an email. If the address is right, the page is gone; use the site search rather than guessing addresses.
If it is your server
If a page is gone for good, answer 410 rather than 404: search engines stop returning to such an address noticeably sooner. If it moved, use a 301 to its new address — that address specifically, not the home page: a blanket redirect counts as a soft 404 and does the same harm. And check separately that your own 404 page really answers with a 404 rather than a 200 with pretty text.
Easily confused with
«gone for good, deliberately» — the same meaning to a human, a stronger signal to a crawler.
410 →the resource exists but access is closed. Sometimes a 404 is returned instead of a 403 on purpose.
403 →the address did not vanish, it changed: then it needs a redirect rather than a 404.
301 →How to check
what the code actually is — the page itself will not tell you
which addresses return 404 most often: that is usually where the broken link is
The reference holds sixty-four codes searchable by number, name and meaning — plus a breakdown of confusing pairs such as 401 and 403.
Updated