When a cell contains a formula ISFORMULA will return TRUE regardless of the formula’s output or error conditions.

ISREF Function

The Excel ISREF returns TRUE when a cell contains a reference and FALSE if not.

you’re free to use the ISREF function to check for a reference in a formula.

Excel ISNUMBER function

Excel ISTEXT function

Excel ISERROR function

Excel ISFORMULA function

Excel ISREF function

Excel ISLOGICAL function