The Frogs is a comedy mainly due to its use of satire. Satire is a form of comedy used to ridicule elements of society. Aristophanes was considered a master of satire in his day, often ridiculing political, philosophical, and other major figures.
The Frogs mainly satirizes Athenian society. The master-slave relationship between Dionysus and Xanthias is presented in a way that makes Dionysus the master look foolish. Rather than being bold and brilliant, Dionysus is a coward and a egocentric figure, taking away from his alleged godly glory. Aristophanes also satirizes Euripides, presenting the late playwright as an over-intellectual upstart causing trouble in the underworld, just as his socially conscious plays stirred up controversy during his lifetime.
Another comedic element of the play is farce. Farce is a style of theatrical comedy dominated by exaggerated and absurd situations. The Frogs features several farcical elements, such as Dionysus disguising himself as Heracles to avoid trouble in the underworld only for the disguise to cause him even more grief since Heracles is a disliked figure among the underworld's denizens. He swaps his disguise with his slave Xanthias, but Xanthias receives only benefits and pleasures when wearing it (an absurd situation in and of itself, since he is a slave), making the reversal humorous.