When our monitoring nodes perform a check on a URL, only the first 250kb is downloaded.
If you're using Response Body Content Checking your string must be in the first 250kb of the downloaded web page. Content after the first 250kb is discarded and thus content checking will not work. However, this will not affect alerting on HTTP status, code or response time.
We enforce this hard limit to ensure large web pages do not affect the performance of our backend alerting service. Roughly 98% of web checks configured as of Dec 2015 are less than 250kb, so most configurations will not require modification.
If you're unsure how this limitation will affect any of your service checks, please log in to the StackPath Portal and contact support via our 24x7 live chat or a submit a ticket.