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ArduinoJson - C++ JSON library for IoT

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An elegant and efficient JSON library for embedded systems.

It's designed to have the most intuitive API, the smallest footprint and is able to work without any allocation on the heap (no malloc).

It has been written with Arduino in mind, but it isn't linked to Arduino libraries so you can use this library in any other C++ project. For instance, it supports Aduino's String and Stream, but also std::string, std::istream and std::ostream.


  • JSON decoding (comments are supported)
  • JSON encoding (with optional indentation)
  • Elegant API, very easy to use
  • Fixed memory allocation (zero malloc)
  • No data duplication (zero copy)
  • Portable (written in C++98)
  • Self-contained (no external dependency)
  • Small footprint
  • Header-only library
  • MIT License

Works on

  • Arduino boards: Uno, Due, Mini, Micro, Yun...
  • ESP8266, ESP32
  • Teensy
  • RedBearLab boards (BLE Nano...)
  • Intel Edison and Galileo
  • WeMos boards: D1...
  • Computers: Windows, Linux, OSX...
  • PlatformIO
  • Particle
  • Energia

Quick start

Decoding / Parsing

char json[] = "{\"sensor\":\"gps\",\"time\":1351824120,\"data\":[48.756080,2.302038]}";

StaticJsonBuffer<200> jsonBuffer;

JsonObject& root = jsonBuffer.parseObject(json);

const char* sensor = root["sensor"];
long time          = root["time"];
double latitude    = root["data"][0];
double longitude   = root["data"][1];

See JsonParserExample.ino

Use ArduinoJson Assistant to compute the buffer size.

Encoding / Generating

StaticJsonBuffer<200> jsonBuffer;

JsonObject& root = jsonBuffer.createObject();
root["sensor"] = "gps";
root["time"] = 1351824120;

JsonArray& data = root.createNestedArray("data");

// This prints:
// {"sensor":"gps","time":1351824120,"data":[48.756080,2.302038]}

See JsonGeneratorExample.ino

Use ArduinoJson Assistant to compute the buffer size.


The documentation is available online in the ArduinoJson Website.

The ArduinoJson Assistant helps you get started with the library.


Special thanks to the following persons and companies who made generous donations to the library author:

  • Robert Murphy USA
  • Surge Communications USA
  • Alex Scott United Kingdom
  • Firepick Services LLC USA
  • A B Doodkorte Netherlands
  • Scott Smith USA
  • Johann Stieger Austria
  • Gustavo Donizeti Gini Brazil
  • Charles-Henri Hallard France
  • Martijn van den Burg Netherlands
  • Nick Koumaris Greece
  • Jon Williams USA
  • Kestutis Liaugminas Lithuania
  • Darlington Adibe Nigeria
  • Yoeri Kroon Netherlands
  • Andrew Melvin United Kingdom
  • Doanh Luong Vietnam
  • Christoph Schmidt Germany
  • Prokhoryatov Alexey Russia
  • Google Inc. USA
  • Charles Haynes Australia
  • Charles Walker USA

Found this library useful? Please star this project or help me back with a donation! 😄