Code validation

Overview

Using standards-compliant code increases the likelihood that all web browsers and assistive technologies will correctly handle your content. There are many reasons to validate your code:

• Validating markup increases the likelihood that browsers and assistive technologies will properly handle your content.
• Validating markup can help in your debugging efforts if your web page exhibits unexpected problems.
• Valid markup provides a better cross-browser, cross-platform, experience and gives you maximum control over how your page is displayed.
• Valid markup will help with future compatibility as it will have the best chance of being backward-compatible with new technologies.
• Valid markup renders faster than markup that has errors. This means less load on servers and client browsers.
• A site that validates using proper HTML is a sign of professionalism.

Techniques

• Use the W3C Markup Validation Service to check your HTML against current web standards.
• Use the W3C CSS Validation Service to validate your Cascading Style Sheets.
• Use a variety of the tools listed on our Tools and resources page. Some of the tools listed check for HTML validation in addition to other accessibility issues.

WCAG 2.1 success criteria

The issues described on this page, and associated Techniques pages, map to the following success criteria in the W3C’s Web Content Accessibility Guidelines (WCAG) 2.1:

• 4.1.1 Parsing (Level A) – NOTE: This success criterion was removed from WCAG 2.2 since current browsers and assistive technologies have improved their ability to handle  a variety of HTML code. However, it’s still required under WCAG 2.1, which is the standard adopted by the UW.