In which direction to dig to make masternode monitoring?

Question

API

Probably many of you have already heard about masternodes, so the task was to monitor these masternodes... There
are similar services... for example: https://masternodes.online I found such services, so the question arose of how to file it myself, I don’t even know which way to dig for now ... if someone directs me to the right reading, I will be very grateful.