I know this is an open ended question, but hopefully it will get some good answers before the thread is locked...
I'm wondering what methods there are to programmatically check (language agnostic) if a website is online from a client perspective (assume you can't make changes to the site/server, but you can rely on certain behaviours of the site.)
The result of each method could stack to provide a measure of certainty that the site is up/down - that is, a method does not have to provide a definite indication if the site is up/down on its own.
Some common tests just to check 'upness' may be:
Others I can think of to check that the site is up and functioning:
Check you received a well formed html response i.e. html to html tags, if the site is experiencing trouble it may spit an error and exit without writing the rest of the page (not all that reliable though because the site may handle most errors in a better way)
Check certain content is or is not on the page, i.e. perhaps there is some content that is always present on your pages, or always present in the case of an error
Can anybody think of any other methods that could be used to help determine if a site is in fact up/down and functioning/not functioning correctly from within a program?
If your get request on a page that displays info from database comes back with status 200 and matching keywords are found, you can be pretty certain that your site is up and running.
And you don't really need to write your own script to do that. There are free services such as GotSiteMonitor, Pingdom, UptimeRobot etc. allows you to monitor your site.