There are various online automated checks, such as Cynthia says and Bobby.

It's important to understand, however, that no satisfactory algorithmic accessibility test exists. These tests often flag "errors" which are harmless, and fail to notice severe accessibility problems.

It's also worth noting that some of the WCA guidelines are controversial. For example, I believe that access keys harm accessibility and should never be active by default.

Nevertheless, these tests are worth doing just in case they highlight something you'd forgotten to do.