Mechanic insurance, for whichever mechanic you are
"Mechanic insurance" means three different things: the employed tech asking what the shop's policy covers, the toolbox first; the self-employed mechanic running a one-bay operation that needs the shop stack at small scale; and the mobile mechanic, whose van is the shop. This page sorts out which you are and what each actually needs.
Garage liability vs garage keepersThe employed tech: know where the shop's coverage stops
A tech on a shop's payroll works under the shop's garage liability and, in nearly all states, its workers compensation (NAIC, Insure U: Small Business Insurance). The question that actually bites is the toolbox. A working tech's own tools can represent years of invested income sitting in the shop, and whether the shop's property coverage extends to employees' tools is a policy-specific answer. Ask, in writing, and if the answer is no, individual tool coverage exists. That one question is this page's most practical sentence.
The self-employed mechanic: the stack at one-bay scale
A mechanic running their own bay carries the same working set as any shop, sized down: garage liability for the operations, the garagekeepers conversation whenever customer vehicles sit in your custody, both defined in the forms IRMI documents (garage liability; garagekeepers), property coverage for the equipment, and workers compensation the day a first employee starts. There is rarely a legal minimum forcing any of it on a repair operation, which this site says plainly rather than implying a mandate that does not exist. The full-size version of this stack, underwriting questions included, is on auto repair shop insurance.
Working out of a van instead of a bay changes the shape more than the size: the liability travels, the van needs commercial auto, and the custody question reads differently. That case has its own page, mobile mechanic insurance. And whichever mechanic you are, a claim that the work itself caused harm is its own liability question, faulty work by name, to raise with an agent rather than assume. Not sure where your operation sits? Start at the overview.