mcp-elicitation-mrtr

Stateless Elicitation

A Stateless MCP server demonstrating Stateless Elicitation through multi-round-trip requests (MRTR). The MCP endpoint is /mcp (for example, http://localhost:8787/mcp under wrangler dev).

The increase-counter tool is write-once and stateless. One tool call progresses through two input rounds:

1. The server returns input_required to ask for an amount and seals the current value into requestState.
2. The client retries with the amount. The server seals the current value and accepted amount into new requestState, then asks for confirmation.
3. The client retries with the confirmation and latest requestState. The server verifies and reads that state before returning the ordinary final tool result.

Each retry carries only that round's input responses. The signed requestState carries trusted intermediate data between fresh Worker requests. The tool does not suspend a Worker, store a pending Promise, or share a server instance between requests.

For existing Legacy deployments that require pushed elicitation/create, Durable Object session state, and SSE replay, see the mcp-elicitation Legacy Elicitation example.

Run

Create a local signing secret of at least 32 bytes, then run the Worker:

printf 'MRTR_REQUEST_STATE_KEY=replace-with-at-least-32-random-bytes\n' > .dev.vars
pnpm install
pnpm run dev

Before deploying, store a production secret with wrangler secret put MRTR_REQUEST_STATE_KEY. Do not reuse the local example value.

Connect a Stateless MCP client to http://localhost:8787/mcp, then call:

{
  "name": "increase-counter",
  "arguments": { "current": 10 }
}

Key pattern

const state = context.mcpReq.requestState<CounterRequestState>();

if (!state) {
  return inputRequired({
    inputRequests: {
      amount: inputRequired.elicit({
        message: "By how much should the counter increase?",
        requestedSchema: {
          type: "object",
          properties: { amount: { type: "number" } },
          required: ["amount"]
        }
      })
    },
    requestState: await requestStateCodec.mint(
      { step: "amount", current },
      context
    )
  });
}