The system needs the right data, in the right format
To guide users
Protect the system
Guideline for form validation
Place error messages near fields
Use colour to differentiate errors from normal field states
When possible, accept data formatted in different ways
When possible, filter invalid characters from being entered
When possible, validate a field before input is complete
Input formatting and input masking are two techniques for guiding user input in real time. Input formatting updates the text field as the user types by re-writing the value with a standard format (e.g., adding dashes or parentheses to a phone number). In contrast, input masking provides a visual template with placeholders that the user fills in, showing the full expected format from the start. Formatting is simpler and more reactive, while masking offers clearer guidance, especially for fixed patterns like phone numbers or credit cards.