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Boost.JSON is a portable C++ library which provides containers and algorithms that implement JavaScript Object Notation, or simply "JSON", a lightweight data-interchange format. This format is easy for humans to read and write, and easy for machines to parse and generate. It is based on a subset of the JavaScript Programming Language (Standard ECMA-262). JSON is a text format that is language-independent but uses conventions that are familiar to programmers of the C-family of languages, including C, C++, C#, Java, JavaScript, Perl, Python, and many others. These properties make JSON an ideal data-interchange language.

This library focuses on a common and popular use-case: parsing and serializing to and from a container called value which holds JSON types. Any value which you build can be serialized and then deserialized, guaranteeing that the result will be equal to the original value. Whatever JSON output you produce with this library will be readable by most common JSON implementations in any language.

The value container is designed to be well suited as a vocabulary type appropriate for use in public interfaces and libraries, allowing them to be composed. The library restricts the representable data types to the ranges which are almost universally accepted by most JSON implementations, especially JavaScript. The parser and serializer are both highly performant, meeting or exceeding the benchmark performance of the best comparable libraries. Allocators are very well supported. Code which uses these types will be easy to understand, flexible, and performant.

Boost.JSON offers these features:

The library relies heavily on these well known C++ types in its interfaces (henceforth termed standard types):

The requirements for Boost.JSON depend on whether the library is used as part of Boost, or in the standalone flavor (without Boost):

Using Boost
  • Requires only C++11
  • The default configuration
  • Aliases for standard types use their Boost equivalents
  • Link to a built static or dynamic Boost library, or use header-only (see below)
  • Supports -fno-exceptions, detected automatically
Without Boost
[Warning] Warning

standalone use is deprecated and will be removed in a future release of Boost.JSON.

  • Requires C++17
  • Aliases for standard types use their std equivalents
  • Obtained when defining the macro BOOST_JSON_STANDALONE
  • Link to a built static or dynamic standalone library, or use header-only (see below)
  • Supports -fno-exceptions: define BOOST_NO_EXCEPTIONS and boost::throw_exception manually

When using without Boost, support for <memory_resource> is required. In particular, if using libstdc++ then version 8.3 or later is needed.


To use as header-only; that is, to eliminate the requirement to link a program to a static or dynamic Boost.JSON library, simply place the following line in exactly one new or existing source file in your project.

#include <boost/json/src.hpp>
Standalone Shared Library
[Warning] Warning

standalone use is deprecated and will be removed in a future release of Boost.JSON.

To build a standalone shared library, it is necessary to define the macros BOOST_JSON_DECL and BOOST_JSON_CLASS_DECL as appropriate for your toolchain. Example for MSVC:

// When building the DLL
#define BOOST_JSON_DECL       __declspec(dllexport)
#define BOOST_JSON_CLASS_DECL __declspec(dllexport)

// When building the application which uses the DLL
#define BOOST_JSON_DECL       __declspec(dllimport)
#define BOOST_JSON_CLASS_DECL __declspec(dllimport)

Boost.JSON works great on embedded devices. The library uses local stack buffers to increase the performance of some operations. On Intel platforms these buffers are large (4KB), while on non-Intel platforms they are small (256 bytes). To adjust the size of the stack buffers for embedded applications define this macro when building the library or including the function definitions:

#include <boost/json/src.hpp>
[Note] Note

This library uses separate inline namespacing for the standalone mode to allow libraries which use different modes to compose without causing link errors. Linking to both modes of Boost.JSON (Boost and standalone) is possible, but not recommended.

Boost.JSON has been tested with the following compilers:

  • clang: 3.8, 4, 5, 6, 7, 8, 9, 10, 11
  • gcc: 4.8, 4.9, 5, 6, 7, 8, 9, 10
  • msvc: 14.0, 14.1, 14.2

Quality Assurance

The development infrastructure for the library includes these per-commit analyses:

  • Coverage reports
  • Benchmark performance comparisons
  • Compilation and tests on, Azure Pipelines, Appveyor
  • Fuzzing using clang-llvm and machine learning

As part of our commitment to producing the very finest C++ libraries that application developers can trust, the C++ Alliance has commissioned Bishop Fox to perform a security audit of the Boost.JSON library. The report is linked here:

C Plus Plus Alliance - Boost JSON Security Assessment 2020 - Assessment Report - 20210317


This library wouldn't be where it is today without the help of Peter Dimov for design advice and optimization assistance.