It depends, upon whom is asking and what the tool is. Bikes are a high-priority hobby. I'd hate to be stuck not able to complete a repair because I loaned, say, my hanger alignment gauge. So I might ask that a bike-specific tool be borrowed on-premise, at my home. OTOH, I would probably hand over any of my non-biking tools -- power tools, saws, lawn mower, pipe wrenches, snowblower, whatever -- without a second thought.

Now that i think about it: I guard my work tools, because they earn the bread. I guard my hobby tools, because they provide the relaxation I need. And all the rest I'm pretty open with.