JSON5
JSON superset for humans. Adds: comments, trailing commas, single quotes, unquoted keys, multi-line strings, hex numbers. Aseem Kishore, 2012.
Pitch: JSON is fine for machine-to-machine data exchange, bad as a config format (no comments!). JSON5 fills the gap. Users: Babel config (.babelrc), TypeScript config (tsconfig.json), ESLint config. Not an official standard — every parser handles things slightly differently. Competitors: JSONC (JSON with Comments, VS Code standard), HJSON (more permissive), YAML (more features but whitespace-sensitive), TOML (more own syntax). Modern config trend: TOML (Cargo, pyproject.toml) or YAML (all DevOps), JSON5 lives in the JS ecosystem.