Resource guide
Principle 3: Understandable
Making sure everyone can follow what is happening on your site — what it says, how it behaves, and how to recover from mistakes.
By Calling All Minds·Last updated April 2026
Success criteria
Across readability, predictability, and input assistance.
Level A
The essential baseline.
Level AA
The legal compliance target.
Level AAA
Enhanced understandability criteria.
Principle 3
About this principle
The Understandable principle is about making sure people can comprehend both the information on your site and how the interface works. This matters for everyone, but it is especially important for people with cognitive disabilities, learning differences, and anyone who speaks a different language.
This principle covers three areas: readability (is your content written clearly and is the language identified so assistive technology can pronounce it correctly?), predictability (does your site behave consistently so people know what to expect?), and input assistance (do you help people avoid and recover from errors?).
WCAG 2.2 added three important criteria here that directly address cognitive accessibility: Consistent Help (3.2.6) ensures people can always find support in the same place, Redundant Entry (3.3.7) stops you asking for the same information twice, and Accessible Authentication (3.3.8 and 3.3.9) ensures people do not need to complete cognitive function tests just to log in.
Where to start
Check your error messages. If they say something went wrong without explaining what or how to fix it, that is a 3.3.1 and 3.3.3 failure. Clear, specific error messages are one of the highest-impact improvements you can make to any form.
Guideline 3.1
Readable
Make text content readable and understandable.
Readable
Content language must be programmatically identified and text must be as clear as possible.
Common omission
Many sites forget to set the lang attribute on the <html> element. Without it, screen readers cannot determine which language to use and may pronounce content incorrectly. This is a Level A failure that takes seconds to fix.
Guideline 3.2
Predictable
Make web pages appear and operate in predictable ways.
Predictable
Navigation and functionality must be consistent so users know what to expect.
New in WCAG 2.2
3.2.6 (Consistent Help) is new in WCAG 2.2. If your site provides a way to contact support or get help — such as a phone number, chat widget, or help link — it must appear in the same location on every page where it is shown. This is especially important for users with cognitive disabilities who rely on predictable layouts.
Guideline 3.3
Input Assistance
Help users avoid and correct mistakes.
Input Assistance
Forms must help users understand what is required, prevent errors, and recover from them clearly.
New in WCAG 2.2
3.3.7 (Redundant Entry) and 3.3.8/3.3.9 (Accessible Authentication) are new in WCAG 2.2. Do not ask users to retype information they have already given you. And do not use CAPTCHAs or cognitive puzzles as the only way to log in — these create insurmountable barriers for many disabled users.
AXS Audit
AXS Audit evaluates your website against the full WCAG 2.2 matrix — visual, cognitive, and keyboard criteria that most automated scanners miss. Built by the same team that created this guide.