# nlohmann/json

JSON for Modern C++

Repository: https://github.com/nlohmann/json
Canonical: https://ross.abutalabs.com/products/json
Homepage: https://json.nlohmann.me
Language: C++
License: MIT
License Family: permissive
Topics: json, json-pointer, json-patch, cbor, msgpack, header-only, stl-containers, json-serialization, json-parser, rfc-6901, rfc-6902, rfc-7159, rfc-7049, json-diff, messagepack, rfc-8259, ubjson, json-merge-patch, bson
Last push: 2026-08-25T15:47:39+00:00

## Health v2 (maintenance only)
Score: 67/100 (v2, computed 2026-09-02T17:46:02.011165+00:00)
- activity 99, release rhythm 8, longevity 100
- inputs: {"age_days": 4808, "days_push": 8, "days_rel": 509, "gap_med": null, "n_releases_24m": 1}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 50471, forks 7479 (observed 2026-08-28T04:12:11.784211+00:00)

## What it is
A header-only C++ library providing JSON parsing, serialization, and manipulation with an intuitive STL-like API. It supports JSON Pointer, JSON Patch, JSON Merge Patch, and binary formats such as CBOR, MessagePack, UBJSON, BJData, and BSON.

## Use cases
- parse  from a string or file in c++
- serialize c++ structs to
- convert  to cbor or messagepack
- apply  patch to a document
- read config files as  in c++
- build and modify  objects with stl-like syntax
- deserialize  into custom types

## When to choose
- you need a mature, widely-used, header-only JSON library for C++
- you want intuitive STL-container-like JSON manipulation
- you need binary JSON-like formats (CBOR, MessagePack, UBJSON, BSON, BJData)
- you need RFC-compliant JSON Pointer, Patch, and Merge Patch support

## When to avoid
- you need maximum parsing performance (consider simd)
- you need relaxed JSON parsing such as trailing commas or comments by default
- you work in a language other than C++

## Facets
- artifact type: library
- maturity: stable
- function: serialization, parser
- domain: developer-tools, apis, files
- platform: cpp, cross-platform, windows
- tags: header-only, -pointer, -patch, cbor, messagepack, ub, bson, bjdata, stl-containers, rfc-8259, linux, macos

## Member repositories
- nlohmann/json (main) score 67

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:12:11.784211+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-29T16:19:52.410002+00:00, confidence not recorded.
  - readme: https://github.com/nlohmann/json (fetched 2026-08-28T04:12:11.784211+00:00, sha 5599c2ccae7b)
  - homepage: https://json.nlohmann.me (fetched 2026-08-28T18:11:30.168880+00:00, sha 8f732461812b)
  - site_page: https://json.nlohmann.me/features/ (fetched 2026-08-28T18:11:30.177864+00:00, sha e4ad9ef7b1c0)
  - site_page: https://json.nlohmann.me/features/arbitrary_types/ (fetched 2026-08-28T18:11:30.185934+00:00, sha 6fceb60563f4)
  - site_page: https://json.nlohmann.me/features/binary_formats/ (fetched 2026-08-28T18:11:30.187919+00:00, sha e3f478842697)
  - site_page: https://json.nlohmann.me/features/binary_formats/bjdata/ (fetched 2026-08-28T18:11:30.189460+00:00, sha dcbec842d3ed)
  - site_page: https://json.nlohmann.me/features/binary_formats/bson/ (fetched 2026-08-28T18:11:30.191102+00:00, sha d573d957b2ee)
  - site_page: https://json.nlohmann.me/api/basic_json/ (fetched 2026-08-28T18:11:30.179780+00:00, sha 23d6f074732b)
  - site_page: https://json.nlohmann.me/home/faq/ (fetched 2026-08-28T18:11:30.182136+00:00, sha 62ddf9125ffd)
  - site_page: https://json.nlohmann.me/home/releases/ (fetched 2026-08-28T18:11:30.184129+00:00, sha 308e00925993)
- Data as of 2026-08-30T08:39:29.467469+00:00.