CodeMeta uses JSON-LD to represent and translate between software metadata formats. JSON-LD lead developer Manu Sporny explains how JSON-LD works in this short clip:
The JSON-LD Context File
The current codemeta context file can be found at 
CodeMeta properties are built on and extend software properties from https://schema.org. A list of all properties provided by the current CodeMeta context file can be found on the terms page. Here’s an example codemeta.json file for the codemetar R package.