Tools for developers to create truly open IoT products using standard JavaScript on low cost microcontrollers.
Tools for developers to create truly open IoT products using standard JavaScript on low cost microcontrollers.
Copyright 2017-2026 Moddable Tech, Inc.
Revised: August 5, 2026
Moddable SDK: Version 9.0.0
The Moddable SDK is a combination of development tools and runtime software to create applications for microcontrollers.
Microcontrollers are highly constrained devices compared to modern computers and mobile devices. A typical microcontroller used with the Moddable SDK has about 45 KB of free memory, 1 MB of Flash ROM, and runs at 80 MHz. The Moddable SDK uses many different techniques, both at build time and at run time, to work efficiently on these devices.
The primary programming language for development is JavaScript. The XS JavaScript engine at the center of the Moddable SDK implements the 2026 JavaScript language standard with better than 99% conformance.[1] The constraints of the target microcontroller may limit the number of language features that can be used in combination in a single project.
The JavaScript language implemented in the Moddable SDK is the same language used in web pages and Node.js. The microcontroller that the scripts run on, however, is very different from a personal computer, server, or mobile device. These differences often require a different approach to using JavaScript. The APIs and objects in the Moddable SDK are quite different, being designed with the goal of minimizing memory use. Bring your existing experience with JavaScript, but be prepared to think about performance, code size, and memory use in a different way.[2]
As much as practical, the Moddable SDK is implemented in JavaScript. Portions of the Moddable SDK are implemented in C for performance or direct access to native APIs.[3] There is no C++.
A significant part of building efficient software for microcontrollers occurs at build time. The Moddable SDK contains many tools and options for the build process.[4] Take time to learn about these to get the best results.
[1] See also: XS Conformance
[2] See also: XS Differences
[3] See also: XS in C
[4] See also: Tools, manifest
The Moddable SDK implements network sockets and a variety of standard, secure networking protocols built on sockets including HTTP/HTTPS, WebSockets, MQTT, mDNS, DNS, SNTP, and telnet.
There is also Bluetooth Low Energy (BLE) protocol support for both BLE peripheral and central device development.
Two APIs for building modern user interfaces are available:
The Moddable SDK also includes command line tools for image format conversion, image compression, image rotation, font compression, localization, and more. The build system automatically makes use of these tools.
The Moddable SDK implements a variety of hardware protocols including digital (GPIO), analog, PWM, and I2C. A number of drivers for common off-the-shelf sensors and corresponding example apps are also available.
The xsbug JavaScript source level debugger is a full-featured debugger that supports debugging modules and applications for XS platforms.
Similar to other debuggers, xsbug supports setting breakpoints, browsing source code, and inspection of the call stack and variables. The xsbug debugger additionally provides real-time instrumentation to track memory usage and profile application and resource consumption.
xsdb is a command line (CLI) debugger modeled on gdb. It is valuable for embedded developers already familiar with gdb, for building automated debugging flows, and for LLMs to debug their code.
See also: xsbug documentation See also: xsdb documentation
To do anything with the Moddable SDK, you have to install it on your computer. This involves downloading this repository, installing some development tools, configuring settings over the command line, and building the Moddable SDK tools.
The Getting Started Guide in the documentation directory walks you through the whole process of installing the Moddable SDK.
With the Moddable SDK installed, you can build and run apps on hardware simulators.
To develop for a particular device, you need to install additional tools and SDKs for that device. The setup process for each device is different, but usually involves installing some additional SDKs, drivers, and development tools.
The SDKs and tools for a particular device are not created or maintained by Moddable, but we do provide detailed instructions to help you install them and get started developing for them with the Moddable SDK. The section below provides links to the setup instructions/developer guides for some of the devices we support.
The Moddable SDK includes simulators that run on macOS, Linux, and Windows. These are a great way to get started, and are invaluable as development accelerators.
To use the simulator, you simply need to install the Moddable SDK.
A video demonstration and information about the simulator is available in the Simulator section of the tools documentation.
To use the Moddable SDK with ESP8266-based devices, you need to:
The Moddable SDK supports many devices built on ESP8266, including the devices shown below.
Moddable One[5] |
Node MCU ESP8266[6] |
Moddable Three[7] |
[5] See also: Moddable One Developer Guide, Moddable product page
[6] See also: Using the Moddable SDK with ESP8266
[7] See also: Moddable Three Developer Guide
To use the Moddable SDK with ESP32-based devices, you need to:
The Moddable SDK supports many devices built on ESP32, ESP32-S2, ESP32-S3, ESP32-C3, ESP32-C6 and ESP32-H2, including the devices shown below.
Moddable Six[8] |
Node MCU ESP32[9] |
M5Stack |
M5Stack Fire |
M5Stick C |
M5Atom Matrix |
[8] See also: Moddable Six Developer Guide, Moddable product page
[9] See also: Using the Moddable SDK with ESP32
To use the Moddable SDK with Pico devices, you need to:
The Moddable SDK supports many devices built with the Raspberry Pi Pico, including the boards shown below:
Raspberry Pi Pico W |
Pimoroni Pico Display |
ili9341 |
Adafruit QT Py |
Sparkfun Pro Micro |
LILYGO T-Display |
To use the Moddable SDK with nRF52 devices, you need to:
The Moddable SDK supports many devices built with the nRF52, including the boards shown below:
Moddable Four[10] |
Nordic DK pca10056 |
Sparkfun Pro nRF52840 |
Makerdiary nRF52840 MDK |
seeed XIAO-nRF52840 |
Adafruit ItsyBitsy nRF52840 |
[10] See also: Moddable Four Developer Guide, Moddable product page
To use the Moddable SDK with Gecko devices, you need to:
The following developer resources are also available:
The Moddable SDK supports four Gecko boards, shown below.
Giant Gecko |
Mighty Gecko |
Thunderboard Sense 2 |
Blue Gecko |
To use the Moddable SDK with the QCA4020, you need to:
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