Validation is how a form refuses an answer it cannot use. Some of it you get without doing anything, because each field type already knows what a sensible value looks like. The rest you add per field, either by formatting the value as it is typed or by setting rules that are checked on submit.
What You Get Without Configuring Anything
Each field type validates its own answers:
- Email checks the value looks like an email address.
- Date checks the value is a real date.
- File Upload checks the file's type and size.
- Number checks the value is a number. (A Number field with a mask relies on the mask's shape instead.)
Required Fields
Turn on the Required toggle in a field's settings and the form cannot be submitted until that field has a value. Required fields are marked so respondents can see which ones they have to answer.
A hidden field is not required. If conditional logic is keeping a field out of sight, it is not blocking submission, so a question can be mandatory for some respondents and absent for others.
The Three Settings
Beyond the built-in checks, three settings control what a field will accept:
| Setting | When it applies | What it does |
|---|---|---|
| Required | On submit | Blocks submission while the field is empty |
| Input Masks | As the user types | Formats the value, such as (555) 123-4567 |
| Input Rules | On submit | Checks the value against rules like min:3 or email |
A mask and a rule do different jobs and are often used together. The mask shapes what the user sees while they type; it does not enforce anything. If the format actually matters, pair the mask with a rule that requires it.
Input Masks
Masks format data as it is entered, so a phone number becomes (555) 123-4567 while the respondent types only the digits. Common uses are phone numbers, Social Security numbers, and postal codes, and you can write your own pattern for anything else.
See Input Masks for the token reference and more examples.
Input Rules
Rules cover minimum and maximum length, numeric ranges, date ranges, and specific formats. For anything the built-in rules do not cover, regex: matches the value against a regular expression, which is how you enforce something like an internal ID format.
Rules are checked live: a moment after the respondent stops typing, the field shows whether its value passes, so problems surface while the answer is still on screen rather than at the end.
See Input Rules for the complete reference.
Error Messages
Flow Forms shows a readable message whenever a value is rejected. You can replace it with your own wording on any field, which is worth doing where the default explains what is wrong but not how to fix it.
Tips
- Only require what you genuinely need. Every extra rule is another way for a respondent to get stuck.
- Test with the awkward values, not just the tidy ones: pasted text, leading spaces, and unusual formats.
- When a rule is strict, say so in the field's help text before the respondent trips over it.
- Write error messages that say what a good answer looks like.
Related
- Input Masks - formatting values as they are typed
- Input Rules - the complete rule reference
- Field Types - built-in validation per field type
- Conditional Logic - how hidden fields affect required