Types

`ClientCapabilities`

ClientCapabilities type {
    roots: Map?,
    sampling: Map?
}

Optional capabilities the client advertises during initialization.

roots - Filesystem root listing support
sampling - LLM sampling request support

Example

::types ::mcp::types
caps ::types/ClientCapabilities({roots: {listChanged: true}, sampling: {}})

`ClientInfo`

ClientInfo type {
    name: Str,
    version: Str
}

Client identification sent during the initialize handshake.

Example

::types ::mcp::types
info ::types/ClientInfo({name: "my-app", version: "1.0.0"})

`Prompt`

Prompt type {
    name: Str,
    title: Str?,
    description: Str?,
    arguments: Vec?
}

A prompt template available on the MCP server.

name - Unique prompt identifier
title - Human-readable display name
description - What the prompt does
arguments - List of argument definitions (each with name, description, required)

Example

::prompts ::mcp::prompts
prompts ::prompts/list(session)
prompt first(prompts)
prompt.name // => "code-review"
prompt.arguments // => [{name: "language", required: true}, ...]

`PromptMessage`

PromptMessage type {
    role: Str,
    content: Map
}

A message in a prompt response.

role - Message role: "user" or "assistant"
content - Message content (type + text/image/resource)

Example

::prompts ::mcp::prompts
messages ::prompts/get-prompt(session, "code-review", {language: "hot"})
message first(messages)
message.role    // => "user"
message.content // => {type: "text", text: "Please review..."}

`Resource`

Resource type {
    uri: Str,
    name: Str,
    description: Str?,
    mime-type: Str?
}

A resource available on the MCP server.

uri - Unique resource URI
name - Human-readable name
description - What the resource contains
mime-type - MIME type of the resource content

Example

::resources ::mcp::resources
resources ::resources/list(session)
resource first(resources)
resource.uri  // => "file:///project/README.md"
resource.name // => "README"

`ResourceContent`

ResourceContent type {
    uri: Str,
    text: Str?,
    blob: Str?,
    mime-type: Str?
}

Content returned from reading a resource.

uri - The resource URI
text - Text content (for text resources)
blob - Base64-encoded content (for binary resources)
mime-type - MIME type of the content

Example

::resources ::mcp::resources
contents ::resources/read(session, "file:///project/README.md")
content first(contents)
content.uri  // => "file:///project/README.md"
content.text // => "# My Project\n..."
// Binary resources use content.blob instead of content.text

`ResourceTemplate`

ResourceTemplate type {
    uri-template: Str,
    name: Str,
    description: Str?,
    mime-type: Str?
}

A URI template for parameterized resources.

uri-template - RFC 6570 URI template
name - Human-readable name
description - What the template produces
mime-type - MIME type of the resulting resource

`ServerCapabilities`

ServerCapabilities type {
    tools: Map?,
    resources: Map?,
    prompts: Map?,
    logging: Map?,
    completions: Map?
}

Capabilities the server advertises during initialization.

tools - Server provides callable tools
resources - Server provides readable resources
prompts - Server provides prompt templates
logging - Server supports structured log messages
completions - Server supports argument auto-completion

`ServerInfo`

ServerInfo type {
    name: Str,
    version: Str
}

Server identification received during the initialize handshake.

Accessible via session.server-info after initialization.

Example

session.server-info.name    // => "my-mcp-server"
session.server-info.version // => "2.0.0"

`Session`

Session type {
    url: Str,
    session-id: Str?,
    protocol-version: Str,
    server-info: ServerInfo,
    server-capabilities: ServerCapabilities,
    headers: Map
}

An active MCP session. Created by ::mcp::client/initialize and passed to all subsequent operations.

url - The MCP server endpoint
session-id - Server-assigned session ID (if any)
protocol-version - Negotiated protocol version
server-info - Server name and version
server-capabilities - What the server supports
headers - Pre-built headers for subsequent requests

Example

::mcp ::mcp::client
::types ::mcp::types
session ::mcp/initialize(
  "https://my-server.example.com/mcp",
  ::types/ClientInfo({name: "my-app", version: "1.0.0"}),
  null
)
session.url              // => "https://my-server.example.com/mcp"
session.protocol-version // => "2025-11-25"
session.server-info.name // => "my-server"

`StreamEvent`

StreamEvent type {
    event: Str?,
    data: Any?,
    id: Str?
}

A parsed SSE event from a streaming MCP response.

event - SSE event type (typically "message")
data - Parsed JSON-RPC message (notification, response, etc.)
id - SSE event ID (for resumability)

Example

::tools ::mcp::tools
events collect(::tools/call-stream(session, "analyze", {}))
event first(events)
event.event // => "message"
event.data  // => parsed JSON-RPC message (Map)

`Tool`

Tool type {
    name: Str,
    title: Str?,
    description: Str?,
    input-schema: Map?
}

A tool available on the MCP server.

name - Unique tool identifier
title - Human-readable display name
description - What the tool does
input-schema - JSON Schema for the tool's arguments

Example

::tools ::mcp::tools
tools ::tools/list(session)
tool first(tools)
tool.name         // => "get_weather"
tool.description  // => "Get weather for a location"
tool.input-schema // => {type: "object", properties: {...}}

`ToolContent`

ToolContent type {
    type: Str,
    text: Str?,
    data: Str?,
    mime-type: Str?,
    resource: Map?
}

A single content item in a tool call result.

type - Content type: "text", "image", "resource", or "resource_link"
text - Text content (when type is "text")
data - Base64-encoded data (when type is "image")
mime-type - MIME type of the content
resource - Embedded resource (when type is "resource")

`ToolResult`

ToolResult type {
    content: Vec,
    is-error: Bool?,
    structured-content: Any?
}

Result from calling a tool on the MCP server.

content - Array of content items (text, images, resources)
is-error - Whether the tool execution resulted in an error
structured-content - Optional structured output matching the tool's output schema

Example

::tools ::mcp::tools
result ::tools/call(session, "get_weather", {location: "Portland"})
result.is-error          // => false
first(result.content).text // => "Sunny, 72°F"

::tools