The yo-yo is red with five black dots resembling a ladybug's shell. Ladybug usually attaches it around her hips when she's not using it. The length of the string is unlimited, and can be controlled by willpower. The end of the string has a small red hoop to put around the finger.
The yo-yo has many functions. Ladybug uses it as a weapon, both offensively and defensively, to hit enemies with it like a projectile or tie them up with its string. It works as a grappling hook, which Ladybug can swing from and use to travel far distances. When swung in a circle very quickly, it lights up pink and creates a shield able to deflect and withstand strong attacks. In "Stormy Weather", Ladybug uses the yo-yo's shield to protect herself and Cat Noir from a bus launched at them by tearing a hole through it. Ladybug can swing from it like a grappling hook.
The yo-yo is useful for some of Ladybug's special abilities. It can capture and purify akumas back to normal butterflies. It's also used for Lucky Charm: Ladybug throws the yo-yo in the air, and it releases a pink energy that produces an object that Ladybug uses to save the day.
One side of the yo-yo can slide open, revealing a screen. With this, Ladybug can use the yo-yo as a tracker, a map, a communicator to contact Cat Noir, or a cellular phone. Additionally, it can access the internet, as seen in "Simon Says" and "Pixelator", like when Ladybug is researching.
In concept art and test animation in the 2014 licensing video, the yo-yo appears to have more abilities, like being able to split in half to become a staff, generating a wing-like shield, and exploding like a bomb. These abilities have not yet been seen in the show.
In "Copycat", one side of the yo-yo can be seen with inverted colors (black with red spots) at times, like when Ladybug is using it as a communicator. Thomas Astruc said that it was a mistake that couldn't be fixed.
Antibug also uses a yo-yo like Ladybug's, except that the colors of the yo-yo are inverted to black with red spots.