MCP Server

Model Context Protocol (MCP) server resource kinds for Telo: stdio and Streamable HTTP transports, composable tool/resource/prompt bundles.

Why use this

• Transport-pluggable — the same tool bundle works over stdio (one client per process) or Streamable HTTP (multi-session) without re-declaration.
• Composable bundles — multiple Mcp.Tools bundles can be merged into one transport; one bundle can be referenced by multiple transports.
• Declarative tool entries — argumentsSchema, handler, inputs: mapping, result: mapping, and catches: rendering are all manifest fields.
• Onboarding-friendly — optional instructions field surfaces a server primer to MCP clients on initialize.
• Mount on Http.Server — Mcp.HttpEndpoint is a standard Telo.Mount, slotted under any path prefix.

Kinds

Kind	Purpose
Mcp.StdioServer	stdin/stdout transport (one client per process).
Mcp.HttpEndpoint	Streamable HTTP transport mounted on Http.Server at a path.
Mcp.Tools	Passive bundle of tool entries dispatched via tools/call.
Mcp.Resources	Bundle of resource entries (schema'd in v1, runtime in v2).
Mcp.Prompts	Bundle of prompt entries (schema'd in v1, runtime in v2).

Example

kind: Telo.Application
metadata: { name: my-stdio-mcp, version: 1.0.0 }
imports:
  Mcp: std/mcp-server@0.7.0
  JS: std/javascript@0.5.0
targets: [ !ref Server ]
---
kind: Mcp.StdioServer
metadata: { name: Server }
serverInfo: { name: my-stdio-mcp, version: 1.0.0 }
tools: [ WeatherTools ]
---
kind: Mcp.Tools
metadata: { name: WeatherTools }
entries:
  - name: get_weather
    description: Get current weather for a city.
    argumentsSchema:
      type: object
      properties:
        city: { type: string }
      required: [ city ]
    handler:
      kind: JS.Script
      name: GetWeatherImpl
    inputs:
      city: "${{ request.arguments.city }}"
    result:
      content:
        - type: text
          text: "${{ result.summary }}"

Reference

• Mcp.StdioServer — stdin/stdout transport, instructions, lifecycle.
• Mcp.HttpEndpoint — Streamable HTTP transport, stateful/stateless modes.
• Mcp.Tools — tool-entry fields, inputs: / result: / catches: semantics.

Composition Notes

• Multiple bundles into one transport. tools: [WeatherTools, DatabaseTools] merges entries from both bundles. Duplicate names across bundles throw at init.
• One bundle into multiple transports. Reference the same Mcp.Tools from both Mcp.StdioServer and Mcp.HttpEndpoint — registrations are independent per-transport, no shared runtime state.
• isError vs. catches:. isError: true on result signals a soft tool failure rendered as content. catches: is for actual throws and produces a JSON-RPC error envelope.

Out of Scope for v1

• Mcp.Resources and Mcp.Prompts runtime dispatch — schemas land in v1, controllers in v2.
• Streaming tool content / progress notifications.
• Streamable HTTP idle-session GC and max-sessions cap (sessions live until Http.Server shuts down).
• Server-initiated sampling, roots, OAuth.
• A polymorphic Telo.Mount dispatch protocol — Mcp.HttpEndpoint duck-types register(app, prefix) to satisfy Http.Server's mount loop today.