Tea Tree and Cracked Toenail

Can you tell me if tea tree oil would be good to use on a toenail that has cracked? I don't know what could have caused it.

Tea tree oil is antifacterial and antifungal. It may be useful for controlling fungal infections that could make your nails brittle, but otherwise, unless there is a fungal origin for the problem, tea tree oil is unlikely to help. You need to establish if you do have an infection so you need to see a health care practitioner for a diagnosis.