Pin and inspect MCP protocol versions

mcp-tui asks for protocol 2026-07-28 by default and falls back as far as the server needs. --protocol-version pins what it asks for.

Pin and inspect MCP protocol versions. See which protocol version a server negotiated, pin an older one, and read the multi round-trip input rounds a 2026-07-28 call took.

What did the server negotiate?

mcp-tui --url http://127.0.0.1:8931/mcp server

Name:        acme-support-desk
Version:     1.4.0
Protocol:    2026-07-28

--log-level info adds one Protocol version negotiated line with every attempt: server/discover first on 2026-07-28, then initialize on 2025-11-25 if the server rejected discovery.

Pin a version

mcp-tui --url http://127.0.0.1:8931/mcp --protocol-version 2025-11-25 server

Pin 2025-11-25 when a server’s tools still call the client directly (sampling, elicitation, roots) and fail under 2026-07-28, or when a server does not answer server/discover. Accepted values are 2026-07-28, 2025-11-25, 2025-06-18, 2025-03-26 and 2024-11-05; anything else fails before connecting. The deprecated SSE transport negotiates at most 2025-11-25.

Multi round-trip requests

On 2026-07-28 a server may not call the client mid-request. A tool that needs input answers with input requests instead; the client answers and retries (SEP-2322). mcp-tui runs that loop itself and reports each round:

mcp-tui --url http://127.0.0.1:8931/mcp tool call schedule_callback ticket_id=T-1041 \
  --elicit-stub '{"time":"2026-10-02T15:00:00Z"}'

Tool response:
Callback booked for T-1041: Dana Whitfield (Northwind Labs) on Fri 2 Oct 2026 at 15:00 UTC, calling the number on file.

Input rounds (SEP-2322):
  round 1 · tools/call · 18.4ms · request state: no
    callback_time: elicitation → accept

With --format json the rounds are in rounds. The 2026-07-28 guide covers the other changes: stateless sessions, list caching, standard headers.