The Web Content Accessibility Guidelines (WCAG) is an extensive standard for web development; right now, its current version is 2.1. It is an essential piece of guideline both for specialists and users.
The WCAG version 2.1 has 13 guidelines with many success criteria distributed among three levels to help you create more accessible web-based products. The levels are: A is the easiest, the AA is the most suggested goal, and the AAA is the most strict.
It has four main principles (named POUR):
- Perceivable: the content must be accessible to everyone.
- Operable: the functionality must work on different user inputs (mouse, keyboard).
- Understandable: must be easily understandable (content, structure, functionality).
- Robust: the result must function on different technologies (like screen readers).
Keep in mind that WCAG is just a tool to make accessibility measurable. If you are WCAG compliant, it still (usually) doesn't mean that you are 100% barrier-free.