A library for reading, writing, and applying Json patches.
It is a completely specification-compliant implementation, although it does add its own extensions. See the differences document for details.
There is documentation here on how the library works, how patching works, and how patches are structured.
This project is mainly intended to be an API for other projects to use. However, there are built versions of the library available that include a basic CLI for patching things.
Not only that, but there is a Minecraft mod that implements patching functionality there.
Please see the relevant section in the API documentation.