check if user agent is valid - SERP Analysis

https://51degrees.com/developers/user-agent-tester

https://gs.statcounter.com/detect

https://www.whatismybrowser.com/detect/what-is-my-user-agent/

https://www.whatismyip.net/tools/user-agent-lookup.php

https://explore.whatismybrowser.com/useragents/parse/

https://developer.mozilla.org/en-US/docs/Web/HTTP/Guides/Browser_detection_using_the_user_agent

https://dnschecker.org/user-agent-info.php

https://www.uptrends.com/support/kb/synthetic-monitoring/monitor-settings/user-agents-and-real-browser-checks

https://stytch.com/blog/user-agent-spoofing/

https://deviceatlas.com/blog/list-of-user-agent-strings