Claude Code

MCP – Claude steers the window

While the app runs it serves MCP at http://127.0.0.1:4340/mcp (Streamable HTTP, local only; another port via MB_MCP_PORT). Register it once:

$ claude mcp add --scope user --transport http monsterbrain http://127.0.0.1:4340/mcp

Tool	Does
get_view	folder, mode, active file, open tabs, view, selected text
open_file	open a file (preview tab, or its own tab with new_tab), optional view and a passage to highlight
show_changes	switch to the change view, return the changed files
show_diff	open the diff of one file
open_folder	open another folder

Extensions add tools (deciwa: deciwa_feedback, deciwa_show). If the app is not running, Claude Code reports the server as not connected.

Agent actions – the window hands work to Claude

Actions reach a running Claude Code session through Claude Code channels (research preview). Start that session in a terminal, in the folder Claude works in:

$ scripts/claude-channel.sh

Claude Code starts resources/channel.mjs, which holds GET /channel on the app’s port open and passes every action on. The session whose folder contains the open folder (or lies inside it) gets the action – the last started one if several do. Channels only work in interactive sessions, not with -p or the Agent SDK.

Ctrl Shift A sends “explain this file” (with the selected text). Extensions add their own actions – deciwa: Inform Claude next to the review switch. Actions are only ever started by a click or key. If no session listens for the open folder, monsterbrain offers Start Claude here: it opens a terminal in the folder with the script above (Linux for now), and the action waits up to two minutes for that session.