Yojson: JSON libraries for OCaml

The Yojson libraries parse JSON and JSON5 data into a nested OCaml tree data structures.

Library documentation

The documentation of both Yojson and Yojson-five can be found on OCaml.org.

Examples

A simple example on how to parse JSON from a string literal.

let json_string = {|
  {"number" : 42,
   "string" : "yes",
   "list": ["for", "sure", 42]}|}
(* val json_string : string *)

let json = Yojson.Safe.from_string json_string
(* val json : Yojson.Safe.t *)

let () = Format.printf "Parsed to %a" Yojson.Safe.pp json

The examples directory contains more examples.

Related tooling

Yojson is a pretty common choice for parsing JSON in OCaml, as such it is the base for a number of tools and libraries that are built on top of it.

• ppx_deriving_yojson to automatically generate code that converts between Yojson.Safe.t and custom OCaml types
• ppx_yojson_conv, an alternative to ppx_deriving_yojson from Jane Street with different design decisions
• atd, generates mapping code from .atd specification files and can be used in multiple languages
• jsonm is an alternate JSON parser that parses JSON into a stream of items, so the complete data structure does not have to be in memory.

Help wanted

Yojson is developed and maintained by volunteers — users like you. Various issues are in need of attention. If you'd like to contribute, please leave a comment on the issue you're interested in, or create a new issue. Experienced contributors will guide you as needed.

There are many simple ways of making a positive impact. For example, you can...

• Use the software in your project.
• Give a demo to your colleagues.
• Share the passion on your blog.
• Tweet about what you're doing with Yojson.
• Report difficulties by creating new issues. We'll triage them.
• Ask questions on StackOverflow.
• Answer questions on StackOverflow.
• Discuss usage on the OCaml forums.
• Pick a task that's easy for you.

Check out in particular good first time issues and other issues with which we could use some help.

License

Yojson is licensed under the 3-clause BSD license, see LICENSE.md for details.