The ESP-Prog is one of Espressif’s development and debugging tools, with functions including automatic firmware downloading, serial communication, and JTAG online debugging. ESP-Prog's automatic firmware downloading and serial communication functions are supported on both the ESP8266 and ESP32 platforms, while the JTAG online debugging is supported only on the ESP32 platform.
ESP-Prog can easily connect to a PC with the use of a single USB cable. The PC can then identify the board's downloading and JTAG interfaces (functions) by their port numbers.
Given that the power supply voltage may vary on different user boards, either of the ESP-Prog interfaces can provide the 5V or the 3.3V power supply through pin headers, in order to ensure power compatibility.
More information is available in the datasheet and on the website of Sparkfun.