Content check is a way to check the presence/absence of specific info on the page. It helps to check not just the page itself for accessibility, but the performance of the site too. It is useful for sites with complicated structure - which contain many scripts and data that is stored in database or other off-site storages. In this case, there is possible cases when the page itself is working fine while some of the linked resources are not available - thus, some info on the page is missed.

HostTracker provides tools to solve this problem. You may create ContentCheck task and provide specific keywords for monitoring:

There are several important things on that screen:

Content Check - set of comma-separated keywords to look for.
Advanced Content Check option - useful for immediate detection of the reasons of a problem. In case of appearance of the keyword, the phrase, previous to the keyword, is sent you as the result of the check. For example, you enter keyword exception and select this option. Somehow, on the page appears the statement: Wrong SQL statement on the line 123 exception. In this case, you get an alert saying Wrong SQL statement on the line 123.
Conditions Field - allows to specify conditions for set of keywords. You may set to detect an error in case of presence/absence of all entered keywords, or just any of them.

For monitoring the presence of images, videos, execution scripts - you may choose a keyword from their description, or add a special short script which will return Error or other keyword if something is missed.

Restrictions:
Only first 10 Kb of page are analysed
Only first 120 characters of each line are analysed