FSON ships with more than the library.
Command line
| Tool | What it does |
|---|---|
fson-check | validate, pretty-print, and convert FSON ↔ JSON / JSON5. Ships in every fson package. |
| Shell completion | Bash and Zsh tab-completion for fson-check. |
Editor support
The ffs-lang-tools monorepo provides syntax highlighting for FSON (and FFS-MD, the FFS Markdown dialect) in two ecosystems:
| Deliverable | Ecosystem | Page |
|---|---|---|
vscode-fson | VS Code extension | VS Code — FSON |
vscode-ffsmd | VS Code extension | VS Code — FFS-MD |
highlightjs-fson | highlight.js grammar (web) | highlight.js grammar |
highlightjs-ffsmd | highlight.js grammar (web) | highlight.js grammar |
The VS Code extensions are published by the Fedem publisher on the Visual Studio Marketplace, and the packaged .vsix files and npm tarballs are also on the Downloads page. The FSON highlight.js grammar is what colours the fson ` code blocks on this very site.
All grammars are derived from the normative FSON grammar — the railroad sources — not from memory, and validated against a corpus of real FSON files.

