A tool belt was a special belt used to hold various tools and equipment.
Montgomery Scott wore a tool belt while making various repairs on the USS Enterprise-A in 2287. (TOS comic: "Star Trek V: The Final Frontier")
Cervantes Quinn had a tool belt when he was prepping the Dulcinea for launch in 2268. He stowed it in the equipment locker on the vessel. (VAN - Declassified novella: The Stars Look Down)