NodeMCU is popular firmware for ESP8266 WiFi SoC. When you buy a NodeMCU ESP8266 board, it must have been flashed with the firmware. But, you can also flash it anytime by yourself, for example when you want custom NodeMCU firmware. For complete documentation of NodeMCU, you can see it here . There are a few steps to flash your board firmware. In this example, I use NodeMCU DevKit 1.0 with ESP-12E core which is easy to get in the market. If you use ESP-01, you need to see my other post about the ESP-01 flashing circuit . 1. Build the firmware. The easiest way is to build from the cloud , just follow the steps then the firmware will be sent to your email. 2. Install esptool.py. It is a python application to communicate with the ESP ROM bootloader. You can install it either from python package manager using pip install esptool or download manually from Github repository here . $ git clone https://github.com/espressif/esptool.git There are several other tools that you ca...