I recently built a thin, very fast Swift-Embedded-compatible JSON Encoder/Decoder lib called "Friday the Thirteenth" (JSON = Jason, get it?). Check it out. [New Package] FridayTheThirteenth: super fast & light JSON parser
I'm using it in a WebAssembly project for a Roll20.net custom character sheet built in Swift, and it powers the JSON features of GitHub - gistya/SwiftXState: Pure Swift, Declarative, Harel State-Chart, State Orchestration and Introspection Library · GitHub (see generics-refactor branch)