The swordbreaker was a dagger that had large, deep serrations along one side of the blade, resembling the barbed teeth of a comb and designed to entrap an opponent's blade, allowing a variety of follow-up techniques. Like the triple dagger, the swordbreaker was a rare form of parrying dagger compared to the main-gauche, partly due to the difficulty of crafting such a specialised weapon. One Italian example dated around 1600 can be found in the Wallace Collection in London and has a hilt consisting of a pair of straight quillons and a ring guard.
It is uncertain whether "swordbreakers" could in fact break sword blades as suggested by some scholars, as swords of this era were intended to stand up to substantial forces, well in excess of what could be generated by a fighter's off-hand. Swords are sometimes depicted in Fechtbüchern as withstanding a two-handed attempt to break them (or show off their resilience). Late Renaissance rapiers and smallswords may not be as robust as the cutting swords of earlier times, however, and have indeed been known to break on occasion, so the claim may have more veracity in relation to the typical civilian weapons of this period.
The term is also applied in modern times to the various devices (such as hooks or spikes) found on some bucklers which served the same purpose as the parrying dagger to entrap an opponent's blade.