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ContentItem

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Content item for MCP tool results

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JsonRpcRequest

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JsonRpcResponse

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JsonSchema

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MCPError

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MCP protocol-level errors These follow the JSON-RPC 2.0 error code conventions.

Error code allocation (per 2026-07-28 spec):
  • -32700, -32600..-32603: standard JSON-RPC 2.0
  • -32000..-32019: legacy/implementation-defined (no new allocations)
  • -32020..-32099: reserved for the MCP specification

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ParamDef

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Parameter definition for tool schema

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Params

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RequestId

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Request ID supporting both Int and String per JSON-RPC 2.0 / MCP spec

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ServerCapabilities

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ServerInfo

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Tool

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Core Tool trait following MCP protocol

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ToolCallOutcome

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Outcome of a tool execution. Per the 2026-07-28 MRTR pattern, a tool may either complete normally (Complete) or request additional client input (InputRequired). On retry, the client resubmits with inputResponses and the echoed requestState; the tool then receives those responses via its arguments and returns Complete.

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ToolDefinition

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ToolError

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ToolResult

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Tool execution result following MCP protocol format

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TransportError

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Transport-level errors These occur at the communication layer (network, IO, etc.)

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RequestStateCodec

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pub trait RequestStateCodec {
  fn seal(Self, RequestStatePayload, now~ : Int) -> String
  fn open(Self, String, RequestStateContext, now~ : Int) -> RequestStatePayload?
}

Seals/opens requestState blobs. Implementations MUST be authenticated (AEAD or HMAC) per spec.

now (unix seconds) is passed in by the caller rather than read from a clock inside the codec: it keeps the codec free of a time-package dependency and makes expiry behavior deterministic in tests.

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ActiveSubscription

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pub(all) struct ActiveSubscription {
  filter : SubscriptionFilter
  reply : ReplyHandle
}

One active subscriptions/listen stream. The server holds these so it can route change notifications to the right client stream. Keyed by the subscription id (the listen request's JSON-RPC id, stringified).

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AesGcmStateCodec

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pub struct AesGcmStateCodec {
  key : Bytes
}

AES-256-GCM codec. Holds a 32-byte key only — each seal draws a fresh 12-byte nonce from the OS CSPRNG (@getrandom), so there is no counter state to synchronize across instances and no risk of nonce reuse.

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AesGcmStateCodec::AesGcmStateCodec

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fn AesGcmStateCodec::AesGcmStateCodec() -> AesGcmStateCodec

Construct a codec by reading 32 bytes of OS entropy via @getrandom. Server startup only. Aborts if the OS entropy source is unavailable.

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AesGcmStateCodec::open

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fn AesGcmStateCodec::open(self : AesGcmStateCodec, blob : String, ctx : RequestStateContext, now~ : Int) -> RequestStatePayload?

Declare seal/open as explicit methods on AesGcmStateCodec so trait method promotion is not implicitly relied upon (implicit promotion is deprecated).

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AesGcmStateCodec::seal

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fn AesGcmStateCodec::seal(self : AesGcmStateCodec, payload : RequestStatePayload, now~ : Int) -> String

Declare seal/open as explicit methods on AesGcmStateCodec so trait method promotion is not implicitly relied upon (implicit promotion is deprecated).

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AesGcmStateCodec::with_key

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fn AesGcmStateCodec::with_key(key : Bytes) -> AesGcmStateCodec

Construct a codec with a caller-supplied 32-byte key (e.g. distributed to all instances sharing MRTR state). Aborts if the key is not 32 bytes.

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MCPServer

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pub struct MCPServer {
  name : String
  version : String
  title : String?
  description : String?
  instructions : String?
  auth_config : 
AuthConfig?
  request_state_codec : AesGcmStateCodec?
  clock : () -> Int
  registry : ToolRegistry
  resource_registry : ResourceRegistry
  prompt_registry : PromptRegistry
  subscriptions : Map[String, ActiveSubscription]
}

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MCPServer::MCPServer

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fn MCPServer::MCPServer(name : String, version : String) -> MCPServer

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MCPServer::close_subscription

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async fn MCPServer::close_subscription(self : MCPServer, subscription_id : String) -> Unit

Gracefully close an active subscriptions/listen stream. Sends an empty complete result carrying io.modelcontextprotocol/subscriptionId and removes the subscription. The caller is responsible for any transport-level stream teardown beyond removing the subscription.

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MCPServer::handle_request

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async fn MCPServer::handle_request(self : MCPServer, request_json : String) -> String

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MCPServer::notify_prompts_list_changed

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async fn MCPServer::notify_prompts_list_changed(self : MCPServer) -> Unit

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MCPServer::notify_resource_updated

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

Announce that a specific resource's content changed. Reaches only the subscriptions that listed uri in their resourceSubscriptions filter — this is the 2026-07-28 replacement for the legacy resources/subscribe per-URI push.

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MCPServer::notify_resources_list_changed

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async fn MCPServer::notify_resources_list_changed(self : MCPServer) -> Unit

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MCPServer::notify_tools_list_changed

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async fn MCPServer::notify_tools_list_changed(self : MCPServer) -> Unit

Public server-side notification triggers. Each routes to matching subscriptions/listen streams.

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MCPServer::prompt

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MCPServer::prompt_mrtr

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MRTR-aware prompt registration. The handler receives the full get params and may return InputRequired to ask the client for input before completing.

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MCPServer::resource

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fn MCPServer::resource(self : MCPServer, uri : String, name : String, description : String, mime_type : String, handler : async () -> Result[
ResourceReadResult, 
MCPError]) -> MCPServer

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MCPServer::resource_mrtr

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fn MCPServer::resource_mrtr(self : MCPServer, uri : String, name : String, description : String, mime_type : String, handler : async (Json) -> Result[
ResourceReadOutcome, 
MCPError]) -> MCPServer

MRTR-aware resource registration. The handler receives the full read params and may return InputRequired to ask the client for input before completing.

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MCPServer::resource_template

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fn MCPServer::resource_template(self : MCPServer, uri_template~ : String, name~ : String, description? : String, mime_type? : String) -> MCPServer

Register a resource template for resources/templates/list. Templates are URI patterns the server can read; this call only advertises the template.

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MCPServer::run_http

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async fn MCPServer::run_http(self : MCPServer, port? : Int, path? : String) -> Unit raise 
TransportError

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MCPServer::run_stdio

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MCPServer::tool

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fn MCPServer::tool(self : MCPServer, name : String, description : String, input_schema : Json, handler : async (Json) -> Result[
ToolResult, 
MCPError]) -> MCPServer

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MCPServer::with_auth

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MCPServer::with_clock

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fn MCPServer::with_clock(self : MCPServer, clock : () -> Int) -> MCPServer

Inject a wall-clock source (unix seconds) for MRTR requestState expiry. Production servers should pass a real clock; the default returns 0, which disables expiry enforcement (blobs never expire).

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MCPServer::with_description

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fn MCPServer::with_description(self : MCPServer, description : String) -> MCPServer

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MCPServer::with_instructions

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fn MCPServer::with_instructions(self : MCPServer, instructions : String) -> MCPServer

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MCPServer::with_prompt

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fn[T : 
Prompt] MCPServer::with_prompt(self : MCPServer, prompt : T) -> MCPServer

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MCPServer::with_prompt_mrtr

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fn[T : 
PromptMRTR] MCPServer::with_prompt_mrtr(self : MCPServer, prompt : T) -> MCPServer

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MCPServer::with_request_state_codec

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fn MCPServer::with_request_state_codec(self : MCPServer, codec : AesGcmStateCodec) -> MCPServer

Enable MRTR (Multi Round-Trip Requests) by supplying a requestState codec. When set, handlers may return input_required results and verify requestState on retry. Without a codec, MRTR is disabled.

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MCPServer::with_resource

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fn[T : 
Resource] MCPServer::with_resource(self : MCPServer, resource : T) -> MCPServer

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MCPServer::with_resource_mrtr

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fn[T : 
ResourceMRTR] MCPServer::with_resource_mrtr(self : MCPServer, resource : T) -> MCPServer

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MCPServer::with_title

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fn MCPServer::with_title(self : MCPServer, title : String) -> MCPServer

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MCPServer::with_tool

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fn[T : 
Tool] MCPServer::with_tool(self : MCPServer, tool : T) -> MCPServer

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PromptRegistry

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type PromptRegistry

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ReplyHandle

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pub(all) enum ReplyHandle {
  Stdio(
Queue[String])
  Http(
Queue[String])
}

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RequestStateContext

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pub(all) struct RequestStateContext {
  principal : String?
  request_method : String
  params : Json
}

Context checked by open, computed from the incoming retry request.

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RequestStatePayload

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pub(all) struct RequestStatePayload {
  principal : String?
  expires_at : Int
  request_method : String
  params_digest : String
  state : Json
}

What the server seals into a requestState blob. All fields except state are integrity/replay controls; state is the server's own opaque continuation data (re-derived on retry, never trusted from the client without verification).

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ResourceRegistry

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type ResourceRegistry

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ServerRequest

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pub(all) struct ServerRequest {
  message : String
  reply : ReplyHandle
}

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SubscriptionFilter

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pub(all) struct SubscriptionFilter {
  tools_list_changed : Bool
  prompts_list_changed : Bool
  resources_list_changed : Bool
  resource_subscriptions : Array[String]
}

A subscriptions/listen notification filter (spec §subscriptions). Each field is optional; omitting a field means "not subscribed to that type".

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SubscriptionFilter::empty

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An empty filter (subscribe to nothing) — the default when fields are absent.

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SubscriptionFilter::matches

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Does this filter opt into the given notification kind? A ResourceUpdated(uri) matches only if the subscription listed that URI in its resourceSubscriptions filter.

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ToolRegistry

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type ToolRegistry

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get_number

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fn get_number(json : Json, key : String) -> Result[Double, 
ToolResult]

Extract number from JSON, returning error ToolResult on failure

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get_optional_number

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fn get_optional_number(json : Json, key : String) -> Result[Double?, 
ToolResult]

Extract optional number from JSON

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get_optional_string

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fn get_optional_string(json : Json, key : String) -> Result[String?, 
ToolResult]

Extract optional string from JSON

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get_string

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fn get_string(json : Json, key : String) -> Result[String, 
ToolResult]

Extract string from JSON, returning error ToolResult on failure

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mcp_server

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fn mcp_server(name~ : String, version~ : String) -> MCPServer

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simple_tool

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fn simple_tool(name : String, description : String, handler : (Json) -> 
ToolResult) -> 
ToolWrapper

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tool_fn

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fn[Args : 
Params, Ret : 
ToToolResult] tool_fn(handler : (Args) -> Ret, name~ : String, description~ : String) -> 
ToolWrapper

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