Four-UA Comparison (Methodology)

The Four-UA Comparison is an audit methodology that tests website accessibility using four different user agent identities: an honest unknown research bot, a Googlebot-impersonating UA, a Chrome browser UA, and a ChatGPT-User AI crawler UA. By comparing responses across all four, the methodology detects UA-specific blocking, bot verification, and the GEO Visibility Gap — findings invisible to single-UA testing.