JSON, with room for humans.

FSON is a superset of JSON — and, since v0.9, a pragmatic superset of JSON5 — that adds the things you need when you edit files by hand: comments (nestable), bare keys, a `--` prefix that switches a member off without deleting it, and `%include` for shared defaults. `fson` is its C++ library: parse, query, modify and rewrite an FSON file without losing a single comment.

A superset of JSON & JSON5

A superset of JSON & JSON5 Every JSON document is already valid FSON, and so is almost every JSON5 one. On top: `//` and nestable `/* */` comments, bare identifier keys, trailing commas, hex / Infinity / NaN numbers, single-quoted and `|`-block strings.

Lossless round-trips

Lossless round-trips Load, change one value, save. Comments and their positions, member order, quoted-vs-bare key form, `--` markers and the exact spelling of every number (`1.50` stays `1.50`) all survive the cycle. Nothing throws on bad input.

fson-check, bundled

fson-check, bundled A CLI that validates and reformats FSON, and converts to strict JSON or to JSON5 — `fson-check --json config.fson | jq`. Diagnostics carry file:line:col; a partial parse still prints. Ships in every package.

C++23 build, C++17 API

C++23 build, C++17 API Builds standalone with CMake (≥ 3.20, GCC 12+), embeds via add_subdirectory, or comes in through Conan. The installed public headers stay C++17-compatible. CPack produces 7Z / TGZ / ZIP / DEB / RPM.