The W3 Validator

I am surprised that so few people know about, and use, the W3C validator service. Even people who claim to be professionals in the field.

Using valid HTML makes it easier for browsers to render a page, and thus makes it more likely that a page will be rendered consistently across all browsers. A valid page also make life easier for accessibility tools, such as screen readers for the visually impaired.

So if you are creating HTML, just take the extra little bit of time to run it through the W3C validator. People viewing the resulting pages will thank you for it.