Nagios / Icinga HTTP check plugin used for uptime monitoring.
Official: nagios.org
Send the User-Agent to the API, device, OS, browser, and bot detection come back in one response. Nagios check_http is identified by name when the string matches.
curl -s "https://api.parseapi.com/useragent" \ -H "User-Agent: check_http/v2.0.3 (nagios-plugins 2.0.3)" \ -H "X-Api-Key: $PARSEAPI_KEY"
Real strings from our archive that resolve to Nagios check_http. Each opens a full breakdown.