A site built to web standards should adhere to standards (HTML, XHTML, XML, CSS) and pursue best practices (valid code, accessible code, semantically correct code, user-friendly URLs etc).

In other words, a site built to web standards should ideally be lean, clean, CSS-based, accessible, usable, and search engine friendly.

Some of the advantages of using web standards are accessibility and stability. Not only does this mean allowing the web to be used by people with disabilities, but also allowing web pages to be understood by people using browsers other than the usual ones – including voice browsers that read web pages aloud to people with sight impairments, Braille browsers that translate text into Braille, hand-held browsers with very little monitor space, and other unusual output devices.

Most web standards are generally designed with forward- and backward-compatibility in mind — so that data using old versions of the standards will continue to work in new browsers, and data using new versions of the standards will “gracefully degrade” to produce an acceptable result in older browsers. Because a website may go through several teams of designers during its lifetime, it is important that those people are able to comprehend the code and to edit it easily. Web standards offer a set of rules that every Web developer can follow, understand, and become familiar with: When one developer designs a site to the standards, another will be able to pick up where the former left off.