nlohmann/json

Analysis updated 2026-06-20

★ 49,588C++Audience · developerComplexity · 2/5Setup · easy

Mindmap

mindmap
  root((repo))
    What it does
      Parse JSON text
      Access nested values
      Serialize to JSON
      Binary format support
    Key features
      Single header file
      C++11 compatible
      STL-like containers
    Tech Stack
      C++
      CMake optional
      vcpkg Conan
    Who uses it
      C++ developers
      API integrators
      Systems programmers

mindmap root((repo)) What it does Parse JSON text Access nested values Serialize to JSON Binary format support Key features Single header file C++11 compatible STL-like containers Tech Stack C++ CMake optional vcpkg Conan Who uses it C++ developers API integrators Systems programmers

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What do people build with it?

USE CASE 1

Read a JSON configuration file in a C++ application and access its values using bracket notation.

USE CASE 2

Call a web API from a C++ program, parse the JSON response, and extract specific fields.

USE CASE 3

Serialize C++ objects to JSON and deserialize JSON back into C++ structs for data exchange.

USE CASE 4

Convert structured data between JSON and binary formats like CBOR or MessagePack in C++ code.

What is it built with?

C++CMakevcpkgConan

How does it compare?

	nlohmann/json	ggml-org/whisper.cpp	x64dbg/x64dbg
Stars	49,588	49,440	48,291
Language	C++	C++	C++
Setup difficulty	easy	moderate	moderate
Complexity	2/5	3/5	4/5
Audience	developer	developer	developer

Figures from each repo's GitHub metadata at analysis time.

How do you get it running?

Difficulty · easy Time to first run · 5min

Single header file, just copy json.hpp into your project. No build system changes needed.

In plain English

nlohmann/json is a C++ library that makes working with JSON data feel natural and straightforward. JSON, which stands for JavaScript Object Notation, is a widely used format for storing and exchanging data between programs and APIs, but C++ does not have built-in JSON support the way languages like Python or JavaScript do. This library bridges that gap by providing a json type that you can use in C++ code almost like a native data structure. The library's key design goal is making integration trivially easy. The entire implementation lives in a single header file, json.hpp, which means you just copy or include one file in your project with no separate compilation step, no linking against an external library, and no changes to your build configuration. Once included, you can parse JSON from a string or file, access nested values using bracket notation, create JSON structures by assigning C++ values, and convert between JSON and standard C++ containers like std::vector and std::map. It also supports advanced features like JSON Pointer for addressing nested elements, JSON Patch for describing changes to a JSON document, and several binary serialization formats like CBOR and MessagePack as alternatives to plain text JSON. You would use this library when you are writing a C++ program that needs to read a configuration file, call a web API, parse data from a service, or exchange structured data with another system that uses JSON. It is aimed at developers who want clean, readable code over maximum raw parsing speed. The library requires a C++11-capable compiler and is widely available through package managers like Conan, vcpkg, and most Linux distribution repositories. The tech stack is pure modern C++.

Copy-paste prompts

Prompt 1

Using nlohmann/json in C++, write code to read a JSON file called config.json, access a nested field called server port, and print its value.

Prompt 2

Write C++ code using nlohmann/json to make a struct serializable to and from JSON, including fields for id as int, name as string, and active as bool.

Prompt 3

Show me how to parse a JSON array response from an API using nlohmann/json and iterate over each item to print a specific field.

Prompt 4

Using nlohmann/json, write a C++ function that takes a std::vector of strings and returns it serialized as a JSON array string.

Prompt 5

Write C++ code with nlohmann/json that builds a nested JSON object with a top-level key user containing name and email fields, then serializes it to a string.

Frequently asked questions

What is json?

C++ library that lets you read, write, and work with JSON data as naturally as if it were a built-in data type, no separate build steps, just copy one header file into your project.

What language is json written in?

Mainly C++. The stack also includes C++, CMake, vcpkg.

How hard is json to set up?

Setup difficulty is rated easy, with roughly 5min to a first successful run.

Who is json for?

Mainly developer.

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