HTTP 404 Not Found

What it means

404 is the most common error users encounter and the easiest to misdiagnose. It means "this URL doesn't map to any resource the server is willing to expose." That's different from "the resource was deleted" (use 410) and from "you don't have access" (use 403).

From a monitoring perspective, a 404 on a monitored endpoint almost always means a URL changed in a deploy, a route was removed, or a routing rule (rewrites, CDN config) is misconfigured. If your monitor was 200 yesterday and 404 today, the URL or the routing layer changed.

Common causes

• Route or page was removed in a deploy
• Typo or trailing-slash mismatch in the monitored URL
• CDN routing rule misconfigured (e.g. missing rewrite)
• Dynamic route handler crashed and the framework fell through to the 404 page
• Wrong host header reaching the wrong vhost

How to fix it

1. 1Double-check the URL — including protocol, host, path, and trailing slash
2. 2Inspect deploy logs or routing config for recent changes
3. 3Test the URL directly with curl to rule out the monitor's request shape
4. 4If the resource is permanently gone, return 410 (Gone) instead of 404 for clearer semantics

How Uptimera reports 404

Uptimera flags 404 as down by default. Custom 404 pages that return 200 (a common SEO mistake) will incorrectly look healthy — make sure your 404 page actually returns HTTP 404.

Related codes