How to validate form entries with validation rules

You will learn

How to add validation rules to a form field, which rule types each field type offers, how to choose whether a rule blocks the save or warns, and how the message reaches users on every channel.

This article is for data platform owners and application builders who configure forms.

Prerequisites

A table whose form you can edit, and the steps in How to set up a data entry form for a table.
For expression rules, keep How to write expressions for form conditions and rules open as the syntax reference.

📝 Note: Validation rules apply on every channel that writes into the table: the form dialog, inline editing in the view's table, file imports, and API writes. One rule, configured once, holds everywhere.

1) Open the Validation panel

Open the table and select Edit form.
Select the field you want to validate.
Open Validation in the property panel on the right.

2) Add a rule and choose its type

Add a rule under Validation rules.
Choose the type. Which types are offered depends on the field's data type:

Field type	Rule types offered
Text	Text length, Pattern, Expression
Number	Number range, Expression
Date, Time, Checkbox	Expression

A field can carry several rules. Each is evaluated on its own, and each has its own message and its own severity.

3) Limit the length of a text value

Choose the Text rule type.
Set Min length, Max length, or both.
Set Allow digits to decide whether digits are accepted in the value.
A text rule needs at least one of the two length bounds. A rule with neither blocks the save until you complete it.

4) Limit a number to a range

Choose the Numeric rule type.
Set Min value, Max value, or both.
To enforce 1 through 5 on a rating field, set Min value to 1 and Max value to 5.

5) Match a pattern

Choose the Regex rule type.
Enter the pattern under Regular expression. To require a V followed by six digits:

^V\d{6}$

Set Case insensitive if letter case should be ignored.
Anchor the pattern with ^ and $ when the whole value has to match. A pattern without anchors matches anywhere in the value, so V\d{6} also accepts XXV123456YY.

6) Compare fields with an expression rule

💡 Tip: For any condition or expression field, use the Wand icon to build the expression in a guided no-code popup. You can also type the expression directly.

Choose the Expression rule type.
Enter a Boolean expression that has to hold. To keep an end date on or after its start date:

{End Date} >= {Start Date}

An expression rule is the way to express anything that involves more than one field, or a bound that is itself computed:

{Amount} <= {Budget} {Total} = sum({Q1}, {Q2}, {Q3}, {Q4}) iif({Booking Type} = 'Internal', {Cost Center} notempty, true)

Reference fields by their Name, and use the operators and functions listed in How to write expressions for form conditions and rules.

7) Choose whether the rule blocks the save

Set the rule's message type to Error or Warning.
Error blocks the write. The form dialog holds the submit, and a file import row is rejected.
Warning allows the write. The row saves, and the message is reported alongside the result, including on a successful write.
A rule with no message type set behaves as an error.
Use a warning for a soft rule you want people to see and be able to override, such as an amount above a usual threshold.

8) Write the message users read

Enter the message on the rule.
The message appears next to the field in the form dialog, in the per-row report of a file import, and in the API response, identical in all three.
Write what the user should do, not what the rule tested. Vendor code must be a V followed by six digits, for example V123456. beats Regex validation failed.
A rule with no message falls back to a default message.

9) Save and test with data that fails

Select Save.
Open Add row and enter a value that violates the rule. Confirm the message and whether the submit is held.
Import a small file containing a failing row. Confirm the same message appears in the import result.
Test the passing case as well. A rule that rejects everything reads as a working rule until someone tries valid data.

Which requirements are always errors

Two kinds of violation block the write regardless of any message type you set:

A missing required value. Both the field's own requiredness and a conditional requirement from the form.
A change to a read-only field. The field is locked in the form dialog and in inline editing, and a changed value from a file import or an API write is rejected.

To express a requirement that should warn rather than block, leave the field optional and write an expression rule such as {Cost Center} notempty with the message type set to Warning.

Rule reference

Rule type	Definition name	Settings	Available on
Text length	`text`	`minLength`, `maxLength`, `allowDigits`	Text fields
Number range	`numeric`	`minValue`, `maxValue`	Number fields
Pattern	`regex`	`regex`, `caseInsensitive`	Text fields
Expression	`expression`	`expression`	Every field type

Every rule type also carries the message (text) and the message type (notificationType, either error or warning).

Troubleshooting / FAQs

Q: Save reports an incomplete validation rule. What is missing?
A: The rule has a type but not the setting that type needs: a length bound for a text rule, a value bound for a number rule, a pattern for a pattern rule, or an expression for an expression rule. The message names the fields involved. Complete the rule or remove it.
Q: A rule I configured is not rejecting anything on import.
A: Check whether the field is hidden for those rows by a visibility condition. Rules on a hidden field are skipped for that row. See How to show, hide, and require form fields with conditions.
Q: I edited a rule while a large import was running, and the import used the old rule.
A: Expected. An import applies the form definition as it stood when the job started, so the rules are the same for every row of that file. Re-run the import to apply the new rule.
Q: Which rule type should I use for an email address or a URL?
A: A Pattern rule with a regular expression that matches the format you accept.
Q: Can a warning be turned into an error later?
A: Yes. Change the message type on the rule and save. Rows already stored are unaffected, and the new severity applies to the next write.
Q: My messages appear in one language for every user. Can I translate them?
A: Rule messages are returned as written, in one language, so that the form dialog, the import report, and the API response agree word for word. Per-user translation is planned separately.
Q: Does a validation rule run when nothing on the row changed?
A: Rules are evaluated on every write. A row that is saved without changes is validated against the current rules, so a row that predates a rule can be rejected the next time someone saves it.