How to validate a form field to accept exactly 4 numbers

If you need a form field to accept exactly four numeric digits, this guide walks you through how to configure that using a regular expression (regex) validation rule in Flow.

We want to mark a form as valid only if the input is exactly 4 digits

Any other input should be marked as invalid.

Under the Field Validation Rules tab for your field (e.g., 4Numbers), use the following logic:

Mark form as Valid without message when:

data["4Numbers"]=~"^[0-9]{4}$"

This regex checks that:

You can add an “Otherwise” condition to catch anything that doesn’t match and mark it as invalid. For example:

1 = 1

This always evaluates as true, meaning any unmatched input is invalid by default.