The MB Yellow JB is a 4-string electric bass with a J-style poplar body and a slim maple neck with a laurel fingerboard. The neck profile was designed for easy finger placement, and the offset body is described as comfortable to play. It belongs to Markbass's entry-level range and is finished in the brand's yellow with a black pickguard and chrome control plate.

Two single-coil pickups feed a passive circuit with volume, volume and tone controls. Blending the pickups gives a range of tones, from a brighter, trebly sound with a midrange growl to fuller fingerstyle voicings, and it suits slap playing as well. The scale length is 34 inches with 20 frets.

Being passive, it needs no battery and connects to an amplifier with a standard instrument cable. A bag and a strap are included. Each instrument is inspected individually at the maker's headquarters in Italy. The JB sits alongside PB and short-scale M-Master models in the same Yellow family.