Already a popular library in the Fabric ecosystem, Jankson lets you use provided json data in a way that's much more forgiving for real people than Minecraft's built-in Gson. A forgotten comma is forgiven. Comments are allowed. If a new version of a mod injects new keys, it can preserve the user-written comments of the existing file. It's also a full JSON5 parser, letting you input numbers in hexadecimal, and split long strings across multiple lines. ( JSON5 info here - https://json5.org/ )
Packaged as a self-contained mod, Jankson can take advantage of Fabric's Jar-in-Jar feature, making it easier than ever to use and ship, and it comes Fabric-ready with serializers and deserializers for many Minecraft types preloaded.