askuserquestion-mcp

askuserquestion-mcp

A stdio MCP server exposing Claude Code's AskUserQuestion tool to any MCP-aware host (Crush, Cursor, Claude Desktop, custom agents).

The user is prompted via a small browser-rendered form on an ephemeral loopback port. Selections flow back as the canonical SDK answer string:

Auth method?
OAuth

Languages?
- Go
- Rust

Why this exists

Some MCP hosts (notably Crush at the time of writing) do not yet wire the MCP elicitation/create server→client request, so an MCP server cannot delegate "please ask the user" back up to the host. This package sidesteps that by hosting the picker itself: a tiny loopback HTTP server, an embedded HTML form, no external dependencies on the host's UI.

When hosts eventually implement elicitation, the Resolver seam in internal/server makes it a small follow-up to ship an alternative backend that issues elicitation/create instead of opening a browser.

Install

go install github.com/dreamware-nz/askuserquestion-mcp/cmd/askuserquestion-mcp@latest

Requires Go 1.26+ (matching the charm.land/fantasy / askuserquestion-go baseline).

Use with Crush

Drop this into your crush.json:

{
  "mcp": {
    "askuserquestion": {
      "type": "stdio",
      "command": "askuserquestion-mcp"
    }
  }
}

That's it. Crush will list the server's tool as mcp_askuserquestion_AskUserQuestion and route invocations to this binary. When the model calls it, your browser will open with the question form; click submit and the answer flows back to the agent.

Flags

Logs go to stderr; the JSON-RPC stream owns stdout.

Tool surface

Single tool: AskUserQuestion. Schema, validation, and answer formatting come from dreamware-nz/askuserquestion-go; see that repo for the wire format and limits (1-4 questions, 2-4 options each, header ≤ 12 chars).

How it works

LLM ──tool call──▶ MCP host ──stdio──▶ askuserquestion-mcp
                                              │
                                              ├─ validate input
                                              ├─ bind ephemeral :0 on 127.0.0.1
                                              ├─ render embedded HTML form
                                              ├─ open browser (or print URL)
                                              ├─ block on POST /submit
                                              └─ format answers → CallToolResult ──▶ host ──▶ LLM

Only one Ask runs at a time per process; concurrent calls serialize on the Resolver mutex. The HTTP server is torn down at the end of each call so nothing is left listening between turns.

Cancellation semantics

• User closes the browser tab → no signal until ctx times out. The agent context typically cancels the call when the user cancels the turn, which propagates correctly.
• Resolver returns ErrResolverCancelled → non-error tool result [cancelled by user] so the conversation stays valid.
• Validation failure → tool result with IsError=true so the model can self-correct on the next turn.

Security

• Listener binds to 127.0.0.1 by default; never exposed beyond loopback unless you pass --host.
• Form payload is read once per Ask; the server shuts down immediately after.
• No persistence, no caching, no auth (loopback-only).

License

MIT.