In SignNow, can I set up data-validation for fillable-fields via API?

Yes. If you are adding text-tags to add fillable-fields into a SignNow document, you can add data-validation to some of those tags. Tags-formating can contain a data-validator's ID as described in tags documentation here. To learn what validator-ID you need for a certain field, please go over the list of our existing data-validators here.

Watch the SignNow API in action: