Use understandable, well-timed error messages and logical validation rules. If a form field is not filled out correctly, it should be clear to everyone what is wrong.
Please read Accessible feedback in forms, step-by-step first, which explains how to prevent errors, indicate them, and provide help with error messages in a form for different types of users. Another good writeups are A Guide To Accessible Form Validation by Sandrina Pereira on Smashing Magazine and 10 Design Guidelines for Reporting Errors in Forms by Rachel Krause for the NN Group.
Pages in: Feedback on errors
Accessible feedback in forms
How to offer feedback in forms in an accessible way. When you put care into preventing errors and clearly indicating when something goes wrong, users are much more likely to successfully submit a form.
Check at the right moment
To help users and not confuse them, it’s important to choose the right moment to validate user input.
HTML form validation
At this time (2026), form validation by the browser is not sufficiently accessible.
Best message location
For error messages, the best location is above the form field.
Use text for error messages
Always write out the error message in text with clear, plain language.
Write clear error messages
A custom-written error message gives the user the most guidance.
Error summary
A user-friendly way to display errors is a combination of a summary above the form and repeating the error message for each form field.
Screen reader feedback
There are several ways to provide feedback to screen reader users on form errors
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