# How to write a JSON service?

\*If you want to communicate with a client side Eliom program, you do not need to serialize yourself your data to JSON. Serialization/Deserialization of any OCaml type is done automatically by Eliom. Just use OCaml services (or, simpler: server functions and call the function from your OCaml client side program). \*If you want to use your own JSON format, you need to have your own serialisation function to JSON (or for example to use some OCaml library like [yojson](http://mjambon.com/yojson.html) to generate JSON). In that case, you can register your service using `Eliom_registration.String` instead of `Eliom_registration.Html` (see example below). The handler function must return the JSON value as a string, and a the content-type. \*It is even possible to define yourself your own registration module, to be used instead of `Eliom_registration.String`. Thus, you can use an OCaml representation of the JSON value (and you don't call the serializer yourself). Have a look on how modules like `Eliom_registration.String` are implemented to know how to do that.

```ocaml

let my_json_service =
  Eliom_service.create
    ~path:(Eliom_service.Path ["my_json_service"])
    ~meth:(Eliom_service.Get Eliom_parameter.unit)
    ()

let _ =
  Eliom_registration.String.register
    ~service:my_json_service
    (fun () () ->
      Lwt.return ("{text:'something'}", "application/json"))

```
**Comments:** <br/> If you want to get result from a Database, it could already be in JSON format. <br/> Anyway, you probably do not need to pretty-print JSON yourself. <br/>