You've just finished your website and it looks and functions just as you imagined it. You're finished development and are about to release it to the public. Before you do, you should check if it is up to standards. Are there any errors in the code that you might have missed? Here are some tools to make sure your code is as good as it should be.
This validator is being maintained by the W3C community. It checks for errors in your HTML.
Also maintained by the W3C, this checks for errors in your CSS.
3. JS Lint
GTmetrix checks your website for speed issues, and it also includes Yslow and PageSpeed. Your code may be error-free, and your website may run, but does it run fast? If users don't see your website in the first two seconds, they're not going to see it at all.