JSON for Modern C++

JSON for Modern C++

JSON for Modern C++ is a header-only C++11 library that turns JSON into a first-class C++ data type, using the operator magic of modern C++ so that creating, reading, and modifying JSON values feels as natural as it does in languages like Python. The whole library is available as a single header, json.hpp, with no dependencies, no subproject, and no complex build system to set up; a companion header, json_fwd.hpp, provides forward declarations to keep compile times down. See header-only integration for details. It is heavily unit-tested with 100% code coverage, checked with Valgrind and the Clang Sanitizers for memory leaks, and continuously fuzz-tested by Google OSS-Fuzz.

Quick start

Add the single header to your project and use the library like this:

#include <iostream>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

int main()
{
    // parse a JSON string
    json j = json::parse(R"({"happy": true, "pi": 3.141})");

    // access and modify values
    j["name"] = "Niels";
    j["list"] = {1, 0, 2};

    // serialize with an indent of 4 spaces
    std::cout << j.dump(4) << '\n';
}

Get the library by copying the single header json.hpp from the releases page into a directory nlohmann on your include path, or by installing it with a package manager:

brew install nlohmann-json    # Homebrew
vcpkg install nlohmann-json   # vcpkg

find_package(nlohmann_json 3.12.0 REQUIRED)
target_link_libraries(myproject PRIVATE nlohmann_json::nlohmann_json)

See Integration for CMake in detail, all supported package managers (Conan, Meson, Bazel, Conda, and more), and pkg-config.

Explore the documentation

!!! info “Unreleased changes”

This documentation is built from the `develop` branch and may describe changes that are not part of a release
yet. Their version numbers are followed by an <span class="unreleased-version">unreleased</span> badge; see
[Releases](home/releases.md) for what shipped in each version.

The library is licensed under the MIT License. The source code, issue tracker, and discussions are on GitHub.