While theoretically you can speed up your site by just blindly following advice from this blog and other sources, it is much better to understand what’s going on on the page and what you’re dealing with. That’s where the tools come in. Some tools give you insight about the network activities going on between the server and the browser (packet sniffers), some help you benchmark code execution on the client (profilers), some even give recommendations specific to performance improvements. You should aim at mastering as many of the tools as possible, because there’s no single one that is The Tool. And that’s not a bad thing, it’s normal, because performance optimization is a multi-discipline activity touching a lot of different aspects of the the development process.