The comments are anchored to the text and stored in the file, so feedback arrives as a structured prompt rather than a paragraph of "in the third section, change…" — and because the agent can request a review and block, the checkpoint happens before it builds on the wrong version.
A local review tool for specs, prompts and design docs. You highlight text in a rendered view and leave comments; they are stored as invisible HTML markers inside the `.md` file itself, so there is no sidecar file, no database and no service — the markdown stays the source of truth. With the MCP server registered, review works in both directions: the agent can pause and ask for yours, or leave anchored comments on a doc you wrote.
- `mdr_request_review` — the agent pauses mid-task, mdr opens the file, and it waits while you highlight and comment; Send N comments delivers a batch, Send N & finish closes the loop
- `mdr_review` — the agent reviews your document and leaves its findings as inline comments anchored to the exact text, with the browser opening so you read them as they arrive
- `mdr_ask` — anchored questions posted into the doc at a fork the agent cannot resolve alone, blocking until you answer
- `mdr_wait` — how the agent holds the session while a review is in progress
- The viewer and commenting themselves, from `npx md-redline /path/to/spec.md` — no MCP required for that half
Node 20 or newer. `npx md-redline /path/to/spec.md` starts the local app and opens it; installing globally gives you `mdr` for a file, a directory, or `mdr --stop`. Register the MCP server with `mdr mcp install` for Claude Code and Claude Desktop, `codex mcp add md-redline -- mdr mcp`, or `gemini mcp add --scope user md-redline mdr mcp` — the `--scope user` flag matters, because Gemini otherwise registers it for the current directory only. For any other client, `mdr` must be on the PATH of the process your client spawns; use the absolute path from `which mdr` when it is not. Update checks run once a day and can be turned off with `NO_UPDATE_NOTIFIER=1`, which is a presence check, so any value disables it.
One command — npm install -g md-redline