Yojson

Yojson is a JSON parsing and encoding library for the OCaml programming language. It provides a simple, well-documented API and a pure OCaml implementation for working with JSON data. The library exposes a json type that represents JSON values as a variant tree and includes options for two interfaces, typically accessed as Yojson.Basic and Yojson.Safe.

Core features include reading JSON from strings, channels, or files; converting JSON values to OCaml data structures and back; producing compact or pretty-printed JSON output; and a set of convenience functions for navigation and manipulation of JSON objects and arrays. Yojson also supports mapping between JSON values and user-defined OCaml types through encoders and decoders, and it offers a ppx deriver (ppx_yojson) that automatically generates to_json and of_json functions for type declarations.

In practice, Yojson is widely used in the OCaml ecosystem and is known for reliability and performance. It has been integrated into larger ecosystems such as Jane Street's Core and Async libraries, though it remains usable in standalone projects as well. The project is released under a permissive open-source license, and ongoing maintenance and updates reflect its role as a standard tool for JSON handling in OCaml. See also: JSON, OCaml, ppx_yojson, Core library.