Creating a solution > Setting options for fields > Defining field validation
Defining field validation
You can select validation options to ensure that data is entered into a field correctly. When validation options are selected, FileMaker Pro displays a message if you enter data incorrectly. For example, you can set an option to require that users enter a value in a field.
To choose field validation options:
1. With the database open, choose File menu > Manage > Database.
2. In the Manage Database dialog box, click the Fields tab.
3. If your database contains more than one table, select the appropriate table from the Table list.
4. Select an existing field or define a new one.
5. Click Options (or double-click the field name).
6. In the Options for Field dialog box, click the Validation tab.
7. For Validate data in this field, choose Always for ongoing field validation, or Only during data entry to limit validation to instances when data is being entered. Select Allow user to override if you want the user to override validation warnings.
To require that the entered value
Contains only numbers
Strict data type, then choose Numeric Only from the list
Is a date containing numeric values for the month and day, and four digits for the year (for example, 5/12/2014)
Strict data type, then choose 4-Digit Year Date from the list
Is a time containing numeric values for hours and minutes between 00:00 and 23:59 (seconds are not evaluated for this data type validation)
Strict data type, then choose Time of Day from the list
Is not blank
Not empty
Does not duplicate a value found in this field in other records
Unique value
Matches another value in the same field in any other record
Existing value
Matches a value in a specified value list
Member of value list, then choose a value list. (Choose Manage Value Lists to create a list.)
Is within a specific range of letters (alphabetically), numbers, dates, or times
In range, then type the beginning and ending values
Matches the result of a calculation
Validated by calculation (or click Specify), then enter a calculation. See Defining calculation fields for information about the dialog box.
Select or clear Validate only if field has been modified, then click OK.
Does not exceed specified number of characters
Maximum number of characters, then type the maximum number of characters allowed
Does not exceed a specified file size (for container field)
Maximum number of kilobytes, then enter the number of kilobytes. This setting limits the size of a file that’s embedded in a container field or stored externally. This setting has no effect on files that are stored by reference in a container field.
8. To display a custom message if validation fails, select Display custom message if validation fails. Type a message (up to 255 characters).
9. Click OK to close the Options for Field dialog box, or click another tab to set additional field options.
Field and validation values must be identical to successfully validate the contents of a field. If the Validation by calculation option is used, the calculation results must exactly match the contents of the field being evaluated. By default, FileMaker Pro calculates to 16 digits of precision to the right of the decimal. If you are validating fields by calculation that return fractional results, you can use the Round function to limit calculation results to an expected number of digits.
You can also specify the auto-complete option for text fields to help ensure accuracy for data entry. See Setting up a field to auto-complete during data entry.
Unique or existing validation on a field triggers when you exit the field, not when you commit the entire record.
Related topics 
Working with formulas and functions
Entering and changing data in fields
Committing data in records
Defining value lists