FCrDNS

Forward-confirmed reverse DNS: resolve the requesting IP to a hostname, then resolve that hostname back and check it returns the same IP. It is the verification method for crawlers that publish no IP list, and it is the only honest way to test a Googlebot claim.

Crawlers and access

Who is fetching, whether they are who they claim, and what your rules actually permit.

retrieval crawler · user-triggered fetch · verified crawler · forged crawler identity · unverifiable · robots.txt · user-agent group · AI opt-out · Content-Signal · crawl budget · cloaking · challenge page at 200 · uniform refusal · nonexistent-path control · blocked render resource · off-host redirect · homepage refused · Crawler trap · Conditional request · ASN blocking · operator feed · residential proxy · Google-Extended · Google-Agent · GPTBot vs OAI-SearchBot · ClaudeBot vs Claude-User · PerplexityBot vs Perplexity-User · CCBot · Bytespider · agentic traffic · crawler classification

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See it in the full glossary · 579 terms across 19 areas. Scan a site to see which of these apply to it.