How can you test your web server speed?

Our website seems to be slower than it used to be, how can I test that? And is there a way to find the cause? (eg too many visitors).

Thanks.

Solution

There is a rather good tool for performance benchmarking of web servers: Jakarta Jmeter, which is an Apache project, so it's rather well supported and tested.

The key to be able to pinpoint the cause would be to do benchmarking regularly, so you can actually match changes in your benchmark results with events on your server: upgrades, code changes, variations in the number of visitors...