UCL

A high-performance configuration language that extends JSON with Nginx-style syntax, macros, and human-friendly variables.

UCL (Universal Configuration Language) is a robust configuration format designed to bridge the gap between machine-readable JSON and human-editable files. Developed primarily by Vsevolod Stakhov and used extensively in the FreeBSD ecosystem and the Rspamd filtering engine, it supports features like automatic array creation, C-style comments, and human-friendly units: 1k for 1,000 or 10mb for 10,485,760 bytes. The library is written in ANSI C and provides a lightning-fast parser capable of converting UCL objects into JSON, YAML, or MessagePack (making it a versatile choice for complex system configurations).

https://github.com/vstakhov/libucl