Hi, there are uptime monitor services, but now i want to ask if there is any free service which can show me table or graph on how fast my website loads in certain times of the day. + alert me when website loading time is high (can indicate server can be overloaded)

or any linux script?

thank you

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Update:
- this service allows free monitoring of site load time (amongst others) and is usefull for site optimization too! - http://www.showslow.com/
- this service allows monitoring as long as web browser is open: http://webwait.com/
- this service allows onetime page speed test and also monitoring (trial, then paid)