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NodeMCU 2.0.0

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A Lua based firmware for ESP8266 WiFi SOC

NodeMCU is an eLua based firmware for the ESP8266 WiFi SOC from Espressif. The firmware is based on the Espressif NON-OS SDK 2.0.0 and uses a file system based on spiffs. The code repository consists of 98.1% C-code that glues the thin Lua veneer to the SDK.

The NodeMCU firmware is a companion project to the popular NodeMCU dev kits, ready-made open source development boards with ESP8266-12E chips.


  • Easy to program wireless node and/or access point
  • Based on Lua 5.1.4 (without debug, os modules)
  • Asynchronous event-driven programming model
  • 40+ built-in modules
  • Firmware available with or without floating point support (integer-only uses less memory)
  • Up-to-date documentation at

Programming Model

The NodeMCU programming model is similar to that of Node.js, only in Lua. It is asynchronous and event-driven. Many functions, therefore, have parameters for callback functions. To give you an idea what a NodeMCU program looks like study the short snippets below. For more extensive examples have a look at the /lua_examples folder in the repository on GitHub.

-- a simple HTTP server
srv = net.createServer(net.TCP)
srv:listen(80, function(conn)
	conn:on("receive", function(sck, payload)
		sck:send("HTTP/1.0 200 OK\r\nContent-Type: text/html\r\n\r\n<h1> Hello, NodeMCU.</h1>")
	conn:on("sent", function(sck) sck:close() end)
-- connect to WiFi access point
wifi.sta.config("SSID", "password")


The entire NodeMCU documentation is maintained right in this repository at /docs. The fact that the API documentation is mainted in the same repository as the code that provides the API ensures consistency between the two. With every commit the documentation is rebuilt by Read the Docs and thus transformed from terse Markdown into a nicely browsable HTML site at


Due to the ever-growing number of modules available within NodeMCU, pre-built binaries are no longer made available. Use the automated custom firmware build service to get the specific firmware configuration you need, or consult the documentation for other options to build your own firmware.

This project uses two main branches, master and dev. dev is actively worked on and it's also where PRs should be created against. master thus can be considered "stable" even though there are no automated regression tests. The goal is to merge back to master roughly every 2 months. Depending on the current "heat" (issues, PRs) we accept changes to dev for 5-6 weeks and then hold back for 2-3 weeks before the next snap is completed.

A new tag is created every time dev is merged back to master. They are listed in the releases section here on GitHub. Tag names follow the <SDK-version>-master_yyyymmdd pattern.




MIT © zeroday/

Build Options

The following sections explain some of the options you have if you want to build your own NodeMCU firmware.

Select Modules

Disable modules you won't be using to reduce firmware size and free up some RAM. The ESP8266 is quite limited in available RAM and running out of memory can cause a system panic. The default configuration is designed to run on all ESP modules including the 512 KB modules like ESP-01 and only includes general purpose interface modules which require at most two GPIO pins.

Edit app/include/user_modules.h and comment-out the #define statement for modules you don't need. Example:

// #define LUA_USE_MODULES_U8G

Tag Your Build

Identify your firmware builds by editing app/include/user_version.h

#define NODE_VERSION    "NodeMCU 2.0.0+myname"
#ifndef BUILD_DATE
#define BUILD_DATE      "YYYYMMDD"

Set UART Bit Rate

The initial baud rate at boot time is 115200bps. You can change this by editing BIT_RATE_DEFAULT in app/include/user_config.h:


Note that, by default, the firmware runs an auto-baudrate detection algorithm so that typing a few characters at boot time will cause the firmware to lock onto that baud rate (between 1200 and 230400).


To enable runtime debug messages to serial console edit app/include/user_config.h


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