You typically need a full name, business name and/or license number — this information is often on the contractor's website or business card. You can then verify their licensing through the city, county or state (whichever sets regulations for contractors in your area).
To find the specific licensing authority responsible for contractors near you, start with a Google search for “how to check local contractors license in (your location).” For example, where I live in Tulsa, I can verify a plumbing contractor’s license through the Oklahoma Construction Industries Board, which has an easy-to-use search tool.
Most licensed contractors are also bonded, meaning they are legally bound to the work they agreed to do. A bond acts as a sort of insurance to make sure all agreed work is completed on time. You should also make sure your contractor is bonded in case there are disputes with the contractor's progress.
It’s always worth it to check bonds, licenses and insurance. You don’t want to worry about what happens if water goes where it’s not supposed to go.