Safari’s got some increasingly useful developer tools lately, but the menu to access these isn’t shown by default.
Edit: For Safari 3.1, all you need to do is check “Show Develop menu” in Preferences > Advanced. So easy!
To enable the “Develop” menu in Safari on OS X, open a terminal and run the following:
defaults write com.apple.Safari IncludeDebugMenu 1Then restart Safari and you should have to the web inspector, network timeline, awesome user agent selector, and more.
See Apple’s Developer FAQ for more details on developing with Safari.