Reference > Functions reference > Logical functions > IsValid
Returns 0 (false) if the data is invalid; otherwise, returns 1 (true).
field - any field name
Data type returned 
Originated in 
FileMaker Pro 6.0 or earlier
Returns 0 (False) if:
A field contains an invalid value because of a field type mismatch (text in a date field, for example)
FileMaker Pro cannot locate (temporarily or permanently) the related table in which the referenced field is defined
A field has been deleted from a related table, and therefore the references to that field in the source table are invalid
Otherwise, it returns 1 (the data is valid).
Note  IsValid does not check field validation options defined in the Manage Database dialog box. Define field validation options to make sure that data is correctly entered into fields during data entry and import. See Defining field validation.
IsValid(Datefield) returns 0 if there is non-date data in Datefield, for example if text was imported into it.
IsValid(Amount) returns 0 if there is only text in the number field Amount.
IsValid(table::field) returns 0 if the related table was renamed and the relationship isn’t updated with the new filename.
Related topics 
Functions reference (category list)
Functions reference (alphabetical list)
About formulas
About functions
Defining calculation fields
Using operators in formulas