Elicitation And Sampling

Handle interactive server-initiated requests — when the MCP server needs human input during tool execution.

How Requests Arrive (per protocol revision)

The wire mechanics depend on the negotiated MCP revision; the terminal experience is identical either way:

• MCP 2025-11-25 (legacy): the server sends its own JSON-RPC requests (elicitation/create, sampling/createMessage, roots/list) on the active stream and mcp2cli answers inline.
• MCP 2026-07-28 (modern): servers no longer send requests. Instead a tools/call / resources/read / prompts/get may return an interim result with resultType: "input_required" whose inputRequests map embeds the same request shapes (Multi Round-Trip Requests, SEP-2322). mcp2cli prompts you exactly as before, then retries the original request with your answers in inputResponses — echoing the server’s opaque requestState verbatim and using a fresh request id, as the spec requires. Up to 8 round trips are resolved per command before mcp2cli gives up.

The same applies to elicitations that arrive inside a task: when a 2026-07-28 task reaches input_required, mcp2cli prompts and submits the answers via tasks/update (see Background Jobs).

Elicitation

What Is It?

During a tool call, the server may send an elicitation/create request asking the user for additional information — a form with fields, or a URL to visit.

How It Looks

--- elicitation request ---
Please provide additional information:
  Name (Your full name) [required]: John Doe
  Age [required] [default: 25]: 30
  Role [options: admin, user, guest]: admin
--- end elicitation ---

Type Coercion

mcp2cli automatically coerces typed input:

Defaults

When a field has a default value from the schema, pressing Enter without input uses the default.

URL Mode

If the elicitation contains a URL (e.g., for OAuth), mcp2cli opens it in the browser:

auth:
  browser_open_command: "xdg-open"    # Or "open" on macOS

Sampling

What Is It?

The server may send a sampling/createMessage request during tool execution, asking the client for a model response. In mcp2cli, this becomes a human-in-the-loop prompt — you are the “model.”

How It Looks

--- sampling request ---
The server requests a model response.
Model hint: claude-3-5-sonnet
System: You are a helpful assistant
Max tokens: 1000

Messages:
  [user] Summarize this document: ...

Available tools:
  search - Search the knowledge base
  calculate - Perform calculations

Tool choice: auto

Your response (or 'decline' to reject):
--- end sampling ---

Declining

Type decline or press Enter with no input to reject the sampling request. The server receives an error response.

Response

Your text is sent back to the server with model: "human-in-the-loop".

Tool Information

When the server includes tools and toolChoice in the sampling request, mcp2cli displays the available tools and their descriptions so you can make an informed response.

Capability Advertisement

mcp2cli advertises these capabilities during MCP initialization (2025-11-25) or in every request’s _meta["io.modelcontextprotocol/clientCapabilities"] (2026-07-28):

{
  "capabilities": {
    "sampling": {},
    "elicitation": { "form": {}, "url": {} },
    "roots": {},
    "extensions": { "io.modelcontextprotocol/tasks": {} }
  }
}

This tells the server it may request elicitation, sampling, and roots input — and, on 2026-07-28 servers, that task-augmented responses are accepted. Per the MRTR rules, a 2026-07-28 server MUST NOT embed an input request the client did not declare support for.

Note: MCP 2026-07-28 deprecates the Sampling and Roots features (SEP-2577) with a 12-month removal window. mcp2cli continues to answer both for as long as servers use them.

Non-Interactive Mode

In scripts and CI/CD, elicitation and sampling prompts block forever waiting for input. Solutions:

1. Pre-supply answers with --input-json: email --input-json '{"subject":"Hi","body":"..."}' send — provides elicitation field answers up front as a JSON object keyed by field name, so no prompt is shown
2. Decline automatically with --non-interactive: email --non-interactive send — declines (or fails) instead of prompting whenever the server elicits or samples
3. Pipe input: echo "value" | email send
4. Use --timeout: email --timeout 30 send — fails after 30s if blocked
5. Server-side: Configure the server to skip elicitation for automated clients

See Also

• Authentication — OAuth flows may use elicitation
• Request Timeouts — prevent blocking in non-interactive mode