Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
grātŭlātōrĭus, a, um, adj. [gratulor], congratulatory (post-class.): epistola, Capitol. Max. et Balb. 17: cena, Jul. Val. Rer. Gest. Alex. 3, 34 al.
Adv.: grātŭ-lātōrĭē, in a congratulatory manner: mirari, Aug. Conf. 8, 6.