Vinnie Falco
Vinnie Falco


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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]), and is currently standardised in[RFC 8259]. 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:

  • Fast compilation

  • Require only C++11

  • Fast streaming parser and serializer

  • Constant-time key lookup for objects

  • Options to allow non-standard JSON

  • Easy and safe modern API with allocator support

  • Optional header-only, without linking to a library

Visit for complete documentation.


  • Requires only C++11

  • Link to a built static or dynamic Boost library, or use header-only (see below)

  • Supports -fno-exceptions, detected automatically

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

  • string_view

  • memory_resource, polymorphic_allocator

  • error_category, error_code, error_condition, system_error


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>

MSVC users must also define the macro BOOST_JSON_NO_LIB to disable auto-linking.


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>

Supported Compilers

Boost.JSON has been tested with the following compilers:

  • clang: 3.5, 3.6, 3.7, 3.8, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14

  • gcc: 4.8, 4.9, 5, 6, 7, 8, 9, 10, 11, 12

  • msvc: 14.0, 14.1, 14.2, 14.3

Supported JSON Text

The library expects input text to be encoded using UTF-8, which is a requirement put on all JSON exchanged between systems by the RFC. Similarly, the text generated by the library is valid UTF-8.

The RFC does not allow byte order marks (BOM) to appear in JSON text, so the library considers BOM syntax errors.

The library supports several popular JSON extensions. These have to be explicitly enabled.

Visual Studio Solution

cmake -G "Visual Studio 16 2019" -A Win32 -B bin -DCMAKE_TOOLCHAIN_FILE=cmake/toolchains/msvc.cmake
cmake -G "Visual Studio 16 2019" -A x64 -B bin64 -DCMAKE_TOOLCHAIN_FILE=cmake/toolchains/msvc.cmake

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


Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at