A tomato knife is a small serrated

Serrated blade

A serrated blade is a type of blade used on saws and on some knives or scissors. It is also known as a dentated, sawtooth, or toothed blade.A serrated blade has a cutting edge that has many small points of contact with the material being cut...

 kitchen knife

Kitchen knife

A kitchen knife is any knife that is intended to be used in food preparation. While much of this work can be accomplished with a few general-purpose knives – notably a large chef's knife, a tough cleaver, and a small paring knife – there are also many specialized knives that are designed for...

 designed to slice through tomatoes. The serrated edge allows the knife to penetrate the tomatoes’ skin quickly and with a minimum of pressure without crushing the flesh. Many tomato knives have forked tips that allow the user to remove the seeds more easily.

Serrations are not required to cut tomatoes – a sharp straight blade works – but the serrations allow the knife to cut tomatoes and other foods even when dull. Compare bread knife and steak knife

Steak knife

A steak knife is a sharp table knife, used for cutting steak. These often feature serrated blades and wooden handles, and are the only sharp knife commonly found at the modern table....

, which are similarly serrated.