What's a good way to check if my ankle is fractured or just sprained?

See the doc: Go to a foot/ankle specialist to get a proper exam. Your doc will physically examine the ankle to check range of motion and localized pain. Xrays will highlight alignment and check for fractures, but if necessary, an MRI would reveal both bone and soft tissue damage. Don't attempt to treat this on your own.

X-ray: You will need and x-ray to see if you have a fracture or if it is just a sprain. If fractured, you will need to be immobilized with a splint, cast, or rigid walking boot depending on the location of the injury. Have it evaluated by your physician to get the appropriate treatment.