:: COMPARE ::
The short answer
403 admits the thing exists and refuses to give it to you. 404 says there is nothing here at all. The twist: a server is explicitly allowed to answer 404 instead of 403 precisely to avoid revealing that a protected page exists.
Side by side
| Aspect | 404 Not Found | 403 Forbidden |
|---|---|---|
| Does it exist? | Not as far as you know | Yes |
| Would signing in help? | No | Sometimes |
| Reveals existence? | No | Yes |
| Can stand in for the other? | Yes — to hide a page | No |
What each one means
404 is the HTTP status code a web server returns when it can be reached perfectly well but has nothing at the address you asked for. The page isn't there — and the code deliberately makes no promise about whether it ever was, or ever will be.
Full definition of 404 →The contrast above sets out how 403 Forbidden differs from 404 on the points that actually matter.