Links for all the boards supported by Arduino IDE
http://arduino.esp8266.com/stable/package_esp8266com_index.json
http://download.dfrobot.top/FireBeetle/package_DFRobot_index.json
https://dl.espressif.com/dl/package_esp32_index.json
https://espressif.github.io/arduino-esp32/package_esp32_index.json
https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json