Blocked by a firewall or bot filter

The request was stopped before it reached the application: a bot filter, a WAF rule or an IP allowlist.

What it usually means

The request was blocked before it reached your application — a bot filter, a WAF rule, or an IP allowlist that does not include our checker. If the site loads in your own browser, allowlist ErrorDetector rather than treating this as downtime.

What to check first

Allowlist the monitoring origin (one IP, in the EU) in the WAF, CDN or hosting firewall.
Cloudflare "Bot Fight Mode" and similar challenges answer with a page that is not your site.
If the site loads in your own browser, this is not downtime: it is a rule about who may look.

How ErrorDetector reports it

The target answered, so this is reported as a failed check, not downtime: the alert names the reason, the uptime percentage is untouched, and a recovery notice follows when the check passes again.

Caught by: httpkeywordapi monitors. Read about the incident management feature.

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Other causes

DNS · DNS resolution failed (NXDOMAIN, no answer) REF · Connection refused TLS · TLS handshake failed (certificate error) RST · Connection reset by peer NET · Host unreachable (no route) T/O · Connection timed out RDR · Redirect loop (too many redirects) KEY · Keyword not found on the page SLOW · Response slower than the limit ASSERT · API response failed its body assertion 401 · HTTP 401 Unauthorized 403 · HTTP 403 Forbidden 404 · HTTP 404 Not Found 429 · HTTP 429 Too Many Requests 500 · HTTP 500 Internal Server Error 502 · HTTP 502 Bad Gateway 503 · HTTP 503 Service Unavailable 504 · HTTP 504 Gateway Timeout