Model Context Protocol in OCaml
anil.recoil.org
1open Mcp
2open Mcp_sdk
3
4(* Helper for extracting string value from JSON *)
5let get_string_param json name =
6 match json with
7 | `Assoc fields -> (
8 match List.assoc_opt name fields with
9 | Some (`String value) -> value
10 | _ ->
11 raise
12 (Failure (Printf.sprintf "Missing or invalid parameter: %s" name)))
13 | _ -> raise (Failure "Expected JSON object")
14
15(* Create a server *)
16let server =
17 create_server ~name:"OCaml MCP Capitalizer" ~version:"0.1.0"
18 ~protocol_version:"2024-11-05" ()
19 |> fun server ->
20 (* Set default capabilities *)
21 configure_server server ~with_tools:true ~with_resources:true
22 ~with_prompts:true ()
23
24(* Define and register a capitalize tool *)
25let _ =
26 add_tool server ~name:"capitalize"
27 ~description:"Capitalizes the provided text"
28 ~schema_properties:[ ("text", "string", "The text to capitalize") ]
29 ~schema_required:[ "text" ]
30 (fun args ->
31 try
32 let text = get_string_param args "text" in
33 let capitalized_text = String.uppercase_ascii text in
34 TextContent.yojson_of_t
35 TextContent.{ text = capitalized_text; annotations = None }
36 with Failure msg ->
37 Logs.err (fun m -> m "Error in capitalize tool: %s" msg);
38 TextContent.yojson_of_t
39 TextContent.
40 { text = Printf.sprintf "Error: %s" msg; annotations = None })
41
42(* Define and register a resource template example *)
43let _ =
44 add_resource_template server ~uri_template:"greeting://{name}"
45 ~name:"Greeting" ~description:"Get a greeting for a name"
46 ~mime_type:"text/plain" (fun params ->
47 match params with
48 | [ name ] ->
49 Printf.sprintf "Hello, %s! Welcome to the OCaml MCP server." name
50 | _ -> "Hello, world! Welcome to the OCaml MCP server.")
51
52(* Define and register a prompt example *)
53let _ =
54 add_prompt server ~name:"capitalize-prompt"
55 ~description:"A prompt to help with text capitalization"
56 ~arguments:[ ("text", Some "The text to be capitalized", true) ]
57 (fun args ->
58 let text =
59 try List.assoc "text" args with Not_found -> "No text provided"
60 in
61 [
62 Prompt.
63 {
64 role = `User;
65 content =
66 Mcp.make_text_content
67 "Please help me capitalize the following text:";
68 };
69 Prompt.{ role = `User; content = Mcp.make_text_content text };
70 Prompt.
71 {
72 role = `Assistant;
73 content = Mcp.make_text_content "Here's the capitalized version:";
74 };
75 Prompt.
76 {
77 role = `Assistant;
78 content = Mcp.make_text_content (String.uppercase_ascii text);
79 };
80 ])
81
82let () =
83 Logs.set_reporter (Logs.format_reporter ());
84 Eio_main.run @@ fun env -> Mcp_server.run_stdio_server env server