mcp-elicitation

MCP Elicitation Demo

An MCP server that uses elicitation — the ability to request additional user input mid-tool-call. The increase-counter tool asks the user to confirm and specify an amount before modifying state.

What it demonstrates

• this.elicitInput() — requesting structured user input during a tool call, built into McpAgent
• JSON Schema for elicitation — defining the shape of the data you need from the user
• Stateful McpAgent — counter state persists across requests via Durable Objects

Running

npm install
npm start

Open the browser for connection instructions. Elicitation requires an MCP client that supports the elicitation/create protocol method — the browser UI cannot handle the interactive prompt. Connect from one of these instead:

• MCP Inspector — npx @modelcontextprotocol/inspector, set transport to Streamable HTTP and URL to http://localhost:5173/mcp
• Claude Desktop / Cursor / Windsurf — add as a remote MCP server at http://localhost:5173/mcp

How it works

Inside a tool handler, call this.elicitInput() to pause execution and request structured input from the client:

export class MyMCP extends McpAgent<Env, State, {}> {
  server = new McpServer({ name: "Elicitation Demo", version: "1.0.0" });
  initialState = { counter: 0 };

  async init() {
    this.server.registerTool("increase-counter", { ... }, async ({ confirm }) => {
      const result = await this.elicitInput({
        message: "By how much do you want to increase the counter?",
        requestedSchema: {
          type: "object",
          properties: {
            amount: { type: "number", title: "Amount" }
          },
          required: ["amount"]
        }
      });

      if (result.action === "accept" && result.content) {
        this.setState({ counter: this.state.counter + Number(result.content.amount) });
      }
    });
  }
}

export default MyMCP.serve("/mcp", { binding: "MyMCP" });

The MCP client receives the elicitation request, prompts the user, and sends the response back. The tool call resumes once the user responds.

Related examples

• mcp — stateful MCP server without elicitation
• mcp-worker — simplest stateless MCP server