Testing websites

[datiswous]

After launching website I like to run it through Nibbler (http://nibbler.silktide.com) to see what improvements I could make. While it only checks 5 pages, it is usually enough to catch some not so obvious issues. And it is always a fun challenge to reach a higher score.
Another tool I use is PageSpeed (https://developers.google.com/pagespeed/#), to see how can I make my websites load faster.
What other tools do you use to check and optimize your websites?

Didn't know these 2.

Problem with nibbler is that it seems it doesn't work with domain sites where the head-domain points to one site.

I have wouterb.be pointing to wouterb.be/wbpress. But I also have: wouterb.be/gs and wouterb.be/gs-b. Nibbler says I only have wouterb.be/wbpress.