Also wrote up the background on Dev.to if anyone wants more context on how it works: [https://dev.to/plaintos_app_fd54e75a054e/i-built-a-free-tool...]

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quinncom 4 hours ago | parent [-]

The article doesn't really get into the details. Does it analyze the user agent and compare it to a list of known bot user agents? What about all the bots that spoof user agent values – does it do something special to detect those?

	▲	plaintosapp 4 hours ago \| parent [-]
		Yes exactly — it matches against a database of 18 known AI bot user agent tokens (GPTBot, ClaudeBot, CCBot, Bytespider etc.) plus their known IP ranges where available. GPTBot for example publishes its IP ranges officially so we can match on both UA and IP. The spoofing problem is the hard one. Bots that fully spoof Chrome headers are invisible to any UA-based tool including this one. The honest answer is that BotCost catches the "polite" bots that identify themselves — which covers the major AI companies (OpenAI, Anthropic, Google, Meta) since they all self-identify. The truly malicious scrapers that spoof identities are a harder problem requiring behavioral analysis. So it's accurate for what it is — catching known AI training and search crawlers — but not a complete bot detection solution.