Yipper (reffered to by Numbuh 2 as Yipper: Dobermans of the Sky in Sooper Secrets and Boomerang Bloopers) is a fictional franchise within the universe of Codename: Kids Next Door. It features a cartoon character resembling a yellow dog with a red nose, who is often seen flying a red plane. Its merchandise includes trading cards, toys, video games, action figures, a television cartoon, and comic books and appears to be predominantly popular with boys such as Numbuh 4 and Numbuh 2. Yipper is not nearly as prominent in the series as Rainbow Monkeys and is seen only briefly in various episodes. Yipper products can be seen as early as Operation: C.A.N.N.O.N., in which Numbuh 2 is seen reading a Yipper comic book and seen in the beginning of Operation: C.R.I.M.E., Hoagie was reading a Yipper Comic book. In Operation: U.N.C.O.O.L., perhaps Yipper's most prominent appearance, Numbuh 42, Numbuh 2's supplier of cards, is revealed to have stolen Yipper Card 78 from a group of nerds, resulting in them turning into zombies, which they apparently do whenever anything is stolen from them. In Operation: K.I.S.S., Numbuhs 1, 3, 4, and 5 are seen watching a Yipper TV show when they wonder where Numbuh 2 is.
- While the rest of Sector V enjoys Yipper, Numbuh 5 is the only one to dislike it, (Numbuh 1 has a Yipper poster on the wall next to his bed; Numbuh 2 has the same poster above his bed, payed in Yipper cards for soda delivers by Lime Ricky, is seen reading Yipper comics throughout the series, and frequently plays it; Numbuh 3 takes an interest in Numbuh 2's game with Numbuh 4 in Operation: U.N.C.O.O.L.; Numbuh 4 plays Yipper with Numbuh 2, as shown in Operation: U.N.C.O.O.L., and was paid in Yipper cards from the bully fights in Operation: M.A.T.A.D.O.R.).
- In Operation: S.L.U.M.B.E.R., Numbuh 35 uses "Yipper" as his password for the entrance to the Code Module, just as how Numbuh 86's password is a reference to Rainbow Monkeys. This may imply that Numbuh 35 is into Yipper, just like how 86 is into Rainbow Monkeys.