Check for form errors at the right moment

To help users and not confuse them, it’s important to choose the right moment to validate user input.

The best moment to validate input is when the user is finished filling out a form field or after submitting the form.

Avoid confusion or irritation

Imagine you’re typing an email address and, after entering just the first character, an error message appears saying “Invalid email address.”

That message only disappears when the entire email address is filled out. This is not only annoying, it can also cause uncertainty and confusion: “What am I doing wrong? I’m not even finished yet, and it’s already wrong!”.

Resources

• For more information about the drawbacks of native HTML form validation, read The problem with live validation and what to do instead by Adam Silver.
• Native HTML form validation still has accessibility issues in 2026, please read HTML form validation for more context.
• NL Design System Guidelines for web forms (Dutch content).