moonbitstack/moonmcp/server

README
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Bearer
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CacheScope
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Cancellations
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Channel
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Client
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Context
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Facts
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FastMCPError
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Lines
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Memory
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Message
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Principal
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Prompt
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Refused
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Resource
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ResourceTemplate
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Scope
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Server
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Tool
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ToolResult
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decode
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decode_option
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text_block

moonbitstack/moonmcp/server does not have a README file

Cancellations

pub struct Cancellations {
  // private fields
}

Which requests a client has withdrawn by notifications/cancelled.

The notification names a request the client already sent, so a transport keeps this beside its read loop: the loop records, the running requests ask.

Cancellations::add

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fn Cancellations::add(self : Cancellations, id : Json) -> Unit

Record that the client no longer wants the answer to request id.

Cancellations::has

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fn Cancellations::has(self : Cancellations, id : Json) -> Bool

Whether the client has withdrawn request id.

Cancellations::new

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fn Cancellations::new() -> Cancellations

Nothing withdrawn yet.

Cancellations::unwatch

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fn Cancellations::unwatch(self : Cancellations, id : Json) -> Unit

Stop waiting to be told: the request is over.

Cancellations::watch

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fn Cancellations::watch(self : Cancellations, id : Json, hook : () -> Unit) -> Unit

Ask to be told when request id is withdrawn. A stream that waits for something other than its own answer, a subscription above all, has no other way to hear about it.

Channel

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pub(all) struct Channel {
  emit : async (Json) -> Unit
  headers : Map[String, String]
  gone : () -> Bool
  subject : String?
  claims : Map[String, Json]
}

What a transport lends one request: the headers that carried it, the way to send a notification before the reply, and whether the caller is still there.

A transport that can carry nothing beside the reply passes Channel::quiet, which is what Server::handle uses.

Channel::new

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fn Channel::new(emit~ : async (Json) -> Unit, headers~ : Map[String, String], gone~ : () -> Bool, subject? : String, claims? : Map[String, Json]) -> Channel

A channel over the transport that carries this request.

Channel::quiet

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fn Channel::quiet() -> Channel

A channel with nowhere to send and no caller to lose.

Scope

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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_cache_scope

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fn Scope::to_cache_scope(self : Scope) -> @moonbitstack/moonmcp/types.CacheScope
CacheScope

The same scope as the wire names it.

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.

This is the form for a caller with no channel of its own, so a handler's progress reports and log messages are dropped. A transport that can carry them calls handle_with.

Server::handle_with

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async fn Server::handle_with(self : Server, message : Json, channel~ : Channel) -> Json?

Answer one message over channel, which carries the request's headers and whatever the handlers send beside the reply.

Server::log_to

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fn Server::log_to(self : Server, logger~ : @moonbitstack/moonlog.Logger
Logger) -> Unit

Write the server's own log through logger (← a structured logger passed in, never reached for globally): a request served, a request refused, a subscription opened. Context::log writes here too, beside the notification it sends, so a client that went away does not take the record with it.

Without one the server keeps no log of its own; the notifications/message its handlers ask for still go to the client.

Server::new

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

Server::notify

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fn Server::notify(self : Server, message : Json) -> Unit

Hand message to every subscription whose filter asked for it. A subscription that has stopped reading its queue is dropped rather than allowed to hold the change.

Server::notify_prompts_changed

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fn Server::notify_prompts_changed(self : Server) -> Unit

Tell every subscription that the prompts changed.

Server::notify_resource_updated

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fn Server::notify_resource_updated(self : Server, uri : String) -> Unit

Tell the subscriptions that asked for uri that it was rewritten.

Server::notify_resources_changed

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fn Server::notify_resources_changed(self : Server) -> Unit

Tell every subscription that the resources changed.

Server::notify_tools_changed

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fn Server::notify_tools_changed(self : Server) -> Unit

Tell every subscription that the tools changed. Registering a tool does this by itself; a server whose tools come and go for reasons of its own calls it when it knows.

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::prompt_context

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

Offer a prompt whose renderer sees the request it serves.

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::resource_context

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fn Server::resource_context(self : Server, uri : String, read : async (@moonbitstack/moonmcp/context.Context
Context) -> @moonbitstack/moonmcp/resources.RawResourceValue
RawResourceValue, name? : String, title? : String, description? : String, mime_type? : String) -> Unit

Offer a resource whose reader sees the request it serves. A read that needs something from the client answers with ResourceResult::input_required instead of contents.

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 worked on as they arrive, each in a task of its own, so a slow tool does not hold up the next call. Replies still leave in the order their requests came in, which is what a client that counts lines expects; a subscription's notifications are the exception, since they are not replies to anything.

notifications/cancelled withdraws the request it names, which the running task sees through its context.

Server::serve_subscription

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async fn Server::serve_subscription(self : Server, id : Json, params : Map[String, Json], channel : Channel, cancellations? : Cancellations, queue? : @moonbitlang/async/aqueue.Queue
Queue[Json]) -> Unit

Serve one subscriptions/listen request until the transport lets go: the acknowledgement first, then every notification the filter asked for, each tagged with the id of the request that opened the stream.

The reply to the request itself is sent by the caller when this returns, and only when it returns of its own accord: a stream cut by the transport has no reply, as the specification has it.

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::template_context

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fn Server::template_context(self : Server, uri_template : String, read : async (Map[String, Json], @moonbitstack/moonmcp/context.Context
Context) -> @moonbitstack/moonmcp/resources.RawResourceValue
RawResourceValue, name? : String, title? : String, description? : String, mime_type? : String) -> Unit

Offer the resources an RFC 6570 template names, read in the request that matched them.

Server::to_asgi

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fn Server::to_asgi(self : Server, path? : String, origins? : Array[String], docs? : String?, theme? : @moonbitstack/moonmcp/docs.Theme
Theme, auth? : @moonbitstack/moonmcp/auth.Bearer
Bearer?) -> (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 2026-07-28 request that offers a progress token, or that opens a subscription, is answered with text/event-stream when the client accepts it: the notifications the handler sends arrive on that stream, and the reply ends it.

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.

docs names the path the documentation page is served at, beside the endpoint: a browser opened on it lists what the server offers and calls it, in both eras of the protocol. It is on at /docs unless told otherwise, as an API framework's interactive docs are; docs=None leaves it off, and a path equal to the endpoint's is ignored. theme picks its look, the moonmcp website's by default. The page carries no credentials of its own.

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.

Server::tool_context

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

Offer a tool that also sees the request it serves (← FastMCP's Context parameter): its identity in _meta, the headers that carried it, the progress token it offered, and whatever the client answered on a retry.

The handler answers with a ToolResult. An ordinary one carries content; ToolResult::input_required carries an ask instead, which the client satisfies and then sends the same call again with inputResponses and requestState, or with an answer if it cannot.

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.

list_changed_notification

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fn list_changed_notification(operation : String) -> Json

The notification that a server's tools, prompts or resources changed.

method_of

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fn method_of(message : Json) -> String?

The method a message names, if it is a JSON-RPC one at all.

params_of

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fn params_of(message : Json) -> Map[String, Json]

The parameters a message carries, empty when it carries none.

request_id_of

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fn request_id_of(message : Json) -> Json?

The id a request carries; None on a notification.

resource_updated_notification

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fn resource_updated_notification(uri : String) -> Json

The notification that one resource was rewritten.

subscription_closed_result

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fn subscription_closed_result(id : Json) -> Json

The reply that closes a subscription the server ended on purpose, carrying the id of the stream so a client can pair it with the request.

Source Files

Install

Download zip

Model Context Protocol servers and clients for MoonBit.

mcpllmagent

moonbitstack

Apache-2.0

github.com/moonbitstack/moonmcp

Updated 8 hours ago

91 downloads

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#Cancellations

#Cancellations::add

#Cancellations::has

#Cancellations::new

#Cancellations::unwatch

#Cancellations::watch

#Channel

#Channel::new

#Channel::quiet

#Scope

#Scope::equal

#Scope::not_equal

#Scope::to_cache_scope

#Scope::to_repr

#Server

#Server::add_prompt

#Server::add_resource

#Server::add_template

#Server::add_tool

#Server::handle

#Server::handle_with

#Server::log_to

#Server::new

#Server::notify

#Server::notify_prompts_changed

#Server::notify_resource_updated

#Server::notify_resources_changed

#Server::notify_tools_changed

#Server::prompt

#Server::prompt_context

#Server::resource

#Server::resource_context

#Server::run_stdio

#Server::serve_lines

#Server::serve_subscription

#Server::template

#Server::template_context

#Server::to_asgi

#Server::tool

#Server::tool_context

#decode

#decode_option

#list_changed_notification

#method_of

#params_of

#request_id_of

#resource_updated_notification

#subscription_closed_result

Source Files

Cancellations

Cancellations::add

Cancellations::has

Cancellations::new

Cancellations::unwatch

Cancellations::watch

Channel

Channel::new

Channel::quiet

Scope

Scope::equal

Scope::not_equal

Scope::to_cache_scope

Scope::to_repr

Server

Server::add_prompt

Server::add_resource

Server::add_template

Server::add_tool

Server::handle

Server::handle_with

Server::log_to

Server::new

Server::notify

Server::notify_prompts_changed

Server::notify_resource_updated

Server::notify_resources_changed

Server::notify_tools_changed

Server::prompt

Server::prompt_context

Server::resource

Server::resource_context

Server::run_stdio

Server::serve_lines

Server::serve_subscription

Server::template

Server::template_context

Server::to_asgi

Server::tool

Server::tool_context

decode

decode_option

list_changed_notification

method_of

params_of

request_id_of

resource_updated_notification

subscription_closed_result