:bowtie: An elegant and efficient JSON library for embedded systems.
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Latest commit 2e7d498 Jan 15, 2017 @bblanchon Set version to 5.8.1


Arduino JSON library

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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

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

See FAQ: Compatibility issues

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

Encoding / Generating

StaticJsonBuffer<200> jsonBuffer;

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

JsonArray& data = root.createNestedArray("data");
data.add(48.756080, 6);  // 6 is the number of decimals to print
data.add(2.302038, 6);   // if not specified, 2 digits are printed

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

See JsonGeneratorExample.ino


The documentation is available online in the Arduino JSON wiki


From Arduino's Forum user jflaplante:

I tried aJson json-arduino before trying your library. I always ran into memory problem after a while. I have no such problem so far with your library. It is working perfectly with my web services.

From StackOverflow user thegreendroid:

It has a really elegant, simple API and it works like a charm on embedded and Windows/Linux platforms. We recently started using this on an embedded project and I can vouch for its quality.

From GitHub user zacsketches:

Thanks for a great library!!! I've been watching you consistently develop this library over the past six months, and I used it today for a publish and subscribe architecture designed to help hobbyists move into more advanced robotics. Your library allowed me to implement remote subscription in order to facilitate multi-processor robots. ArduinoJson saved me a week's worth of time!!

From Reddit user erm_what_:

This is a great library and I wouldn't be able to do the project I'm doing without it. I completely recommend it.

From Reddit user makerhacks:

I am just starting an ESP8266 clock project and now I can output JSON from my server script and interpret it painlessly.

From Twitter user @hemalchevli:

ArduinoJson library should be used as a benchmark/reference for making libraries. Truly elegant.

From GitHub user sticilface:

its a great lib:) and i use it in everything!


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

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