moonbitstack/moonmcp/server

moonbitstack/moonmcp/server does not have a README file

Scope

pub(all) enum Scope {
  Public
  Private
} derive(Eq, @moonbitlang/core/debug.Debug
Debug)

Who may keep a cached list result: any intermediary, or only caches inside the same authorisation context (the cacheScope of a cacheable result).

Scope::equal

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fn Scope::equal(Scope, Scope) -> Bool

Scope::not_equal

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fn Scope::not_equal(x : Scope, y : Scope) -> Bool

Scope::to_repr

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fn Scope::to_repr(Scope) -> @moonbitlang/core/debug.Repr
Repr

Server

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pub struct Server {
  info : @moonbitstack/moonmcp/types.Implementation
Implementation
  instructions : String?
  ttl_ms : Int
  scope : Scope
  // private fields
}

An MCP server (← FastMCP's FastMCP): the tools, resources, resource templates and prompts it offers, and who it says it is.

It speaks both eras of the protocol. A request carrying its protocol version in _meta is served statelessly under the 2026-07-28 revision; an initialize request opens the handshake of the revisions before it. The same server is reached over Streamable HTTP with to_asgi, over stdio with run_stdio, or by any transport of your own through handle.

ttl_ms and scope are the caching hints every list result carries under the 2026-07-28 revision. The presets say "stale at once" and "this caller only", the cautious end of both, since a server that changes what it lists per caller would otherwise leak one caller's list to the next.

Server::add_prompt

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fn Server::add_prompt(self : Server, prompt : @moonbitstack/moonmcp/prompts.Prompt
Prompt) -> Unit

Offer prompt. A second prompt under the same name replaces the first.

Server::add_resource

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fn Server::add_resource(self : Server, resource : @moonbitstack/moonmcp/resources.Resource
Resource) -> Unit

Offer resource at its URI. A second resource at the same URI replaces the first.

Server::add_template

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fn Server::add_template(self : Server, template : @moonbitstack/moonmcp/resources.ResourceTemplate
ResourceTemplate) -> Unit

Offer template; a URI no fixed resource answers is matched against the templates in the order they were added.

Server::add_tool

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fn Server::add_tool(self : Server, tool : @moonbitstack/moonmcp/tools.Tool
Tool) -> Unit

Offer tool. Its input schema is compiled here, so a call is checked against it before the tool runs. A schema that does not compile is a mistake in the program, not in a request, so it aborts now rather than failing the first call. A second tool under the same name replaces the first.

Server::handle

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async fn Server::handle(self : Server, message : Json) -> Json?

Answer one JSON-RPC message, the way every transport does (← the low-level server's message loop). None is the answer to a notification. A message that is not JSON-RPC at all is answered with the error JSON-RPC prescribes, under a null id.

Server::new

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fn Server::new(name : String, version? : String, title? : String, instructions? : String, ttl_ms? : Int, scope? : Scope) -> Server

Server::prompt

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fn Server::prompt(self : Server, name : String, render : async (Map[String, Json]) -> String, title? : String, description? : String, arguments? : Array[@moonbitstack/moonmcp/types.PromptArgument
PromptArgument]) -> Unit

Offer a prompt rendered as one user message (← @mcp.prompt).

Server::resource

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fn Server::resource(self : Server, uri : String, read : async () -> String, name? : String, title? : String, description? : String, mime_type? : String) -> Unit

Offer a resource read as text (← @mcp.resource(uri)).

Server::run_stdio

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async fn Server::run_stdio(self : Server) -> Unit

Serve over the process's standard input and output (← FastMCP's run(transport="stdio")): one message per line each way, until standard input closes. Anything else the program prints belongs on standard error, since standard output carries nothing but messages.

Server::serve_lines

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async fn Server::serve_lines(self : Server, read : async () -> String?, write : async (String) -> Unit) -> Unit

Serve newline-delimited JSON-RPC: read a line with read until it gives None, answer it, and write the reply as one line (← the stdio transport, over any pair of streams). A line that is not JSON is answered with a parse error; a blank one is skipped.

Requests are answered one at a time, in the order they arrive.

Server::template

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fn Server::template(self : Server, uri_template : String, read : async (Map[String, Json]) -> String, name? : String, title? : String, description? : String, mime_type? : String) -> Unit

Offer the resources an RFC 6570 template names, read as text with the parameters the URI matched (← @mcp.resource("users://{id}")). A template that does not parse aborts at registration.

Server::to_asgi

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fn Server::to_asgi(self : Server, path? : String, origins? : Array[String]) -> (async (@moonbitstack/moonasgi/spec.Scope
Scope, async () -> @moonbitstack/moonasgi/spec.Event
Event, async (@moonbitstack/moonasgi/spec.Event
Event) -> Unit) -> Unit)

The server as an ASGI application serving the MCP endpoint at path (← FastMCP's http_app). Run it with mooncat, or mount it beside a moonapi app.

Every message is its own POST, answered with one JSON object, or 202 for a notification. Sessions, the GET stream and DELETE belong to the revisions before 2026-07-28 and are optional there; this server keeps no session, so GET and DELETE answer 405.

A request whose Origin header names another site is refused with 403, as the transport requires against DNS rebinding. An origin passes when its host is the request's own Host, a loopback address, or one listed in origins.

Server::tool

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fn Server::tool(self : Server, name : String, run : async (Map[String, Json]) -> Json, input_schema? : Json, title? : String, description? : String, output_schema? : Json, annotations? : @moonbitstack/moonmcp/types.ToolAnnotations
ToolAnnotations) -> Unit

Offer a tool whose handler returns any JSON value (← @mcp.tool). An object becomes structured content as well as text; anything else becomes text. An error the handler raises becomes a result marked isError, which the model reads and can correct itself from. A name the protocol does not allow aborts at registration.

decode

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fn[T : @moonbitlang/core/json.FromJson
FromJson] decode(args : Map[String, Json], name : String) -> T raise @moonbitlang/core/json.JsonDecodeError
JsonDecodeError

The argument name of a call, read as T; the code #mcp.tool generates calls this for each required parameter. A string read where something else is wanted is read again as JSON, which is how the {id} of a resource template, always text, reaches an Int parameter.

decode_option

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fn[T : @moonbitlang/core/json.FromJson
FromJson] decode_option(args : Map[String, Json], name : String) -> T? raise @moonbitlang/core/json.JsonDecodeError
JsonDecodeError

The argument name of a call when it may be left out: None when it is missing or null, else the value read as decode reads it. The code #mcp.tool generates calls this for optional parameters.

Source Files

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#Scope

#Scope::equal

#Scope::not_equal

#Scope::to_repr

#Server

#Server::add_prompt

#Server::add_resource

#Server::add_template

#Server::add_tool

#Server::handle

#Server::new

#Server::prompt

#Server::resource

#Server::run_stdio

#Server::serve_lines

#Server::template

#Server::to_asgi

#Server::tool

#decode

#decode_option

Source Files

Scope

Scope::equal

Scope::not_equal

Scope::to_repr

Server

Server::add_prompt

Server::add_resource

Server::add_template

Server::add_tool

Server::handle

Server::new

Server::prompt

Server::resource

Server::run_stdio

Server::serve_lines

Server::template

Server::to_asgi

Server::tool

decode

decode_option