md-redline

Inline review comments for markdown specs, prompts, and design docs.

Highlight text in a rendered document, leave comments, and your AI agent can read and address them directly. Comments are stored as invisible HTML markers in the .md file itself. No sidecar files, no database, no external service. The markdown file stays the source of truth.

With the built-in MCP server, review runs in both directions. Your agent can request your review mid-task and pause until you send your feedback, or review a doc you wrote and leave anchored comments for you. Either way: no copy-paste, no context switching.

See the full review workflow in about 30 seconds:

https://github.com/user-attachments/assets/8b9b3546-a895-42e1-b3cc-5ee5b2c00398

Works with Claude Code, Claude Desktop, Codex CLI, Gemini CLI, and any other MCP client that supports stdio servers. As Sean Grove argues in specs are the new code, specs are becoming the primary unit of work in agentic development. mdr gives that workflow review tooling closer to code review.

Quick start

Prerequisite: Node 20 or newer.

npx md-redline /path/to/spec.md

This starts the local app if needed and opens it in your browser.

Or install globally:

npm install -g md-redline
mdr /path/to/spec.md        # Open a file
mdr /path/to/dir             # Open a directory
mdr --stop                   # Stop the running server
mdr sessions                 # List open review sessions (--kill ID ends one)

md-redline also works as an alias for mdr.

That gives you the viewer and commenting. The agent integration (reviews in both directions, anchored questions) comes from the MCP server, registered in the next section.

Updating

mdr checks npm once a day (from its local server, never blocking anything) and shows a small notice in the viewer and the terminal when a new version is out. Upgrading is one command:

npm install -g md-redline@latest

The running server restarts itself on the next mdr invocation after an upgrade. To disable update checks entirely, set NO_UPDATE_NOTIFIER=1 (or run in CI, which is auto-detected). Note this is a presence check, following the ecosystem convention: any value, even 0 or empty, disables the checks.

MCP setup

Register the MCP server with your agent so it can request reviews mid-task.

Claude Code or Claude Desktop

mdr mcp install                   # register with both clients (default)
mdr mcp install --claude-code     # just Claude Code (via `claude mcp add`)
mdr mcp install --claude-desktop  # just Claude Desktop (JSON config file)

Codex CLI

codex mcp add md-redline -- mdr mcp

Gemini CLI

gemini mcp add --scope user md-redline mdr mcp

The --scope user flag is important. Gemini defaults to per-project scope, which only registers mdr for the current directory.

Other MCP clients

Add this server entry to your client's MCP config file:

{
  "mcpServers": {
    "md-redline": {
      "command": "mdr",
      "args": ["mcp"]
    }
  }
}

Prerequisite: mdr must be on your PATH (e.g. via npm install -g md-redline). If your client spawns subprocesses without inheriting your shell's PATH, use the absolute path from which mdr as the command value.

After installing, restart your MCP client; most clients only discover new servers at launch. To verify, ask your agent "what mdr tools do you have?" and it should list mdr_request_review, mdr_comment, mdr_ask, mdr_wait, mdr_baseline, and mdr_add_files. (mdr_comment was called mdr_review before 0.9; the old name still works if you have it saved in a prompt, but agents are no longer offered it.)

Review workflow

With MCP registered, review runs in both directions. Pick by who is giving the feedback:

	You review the agent's doc	The agent reviews your doc
Typical moment	The agent just drafted or edited a spec; you want to mark it up before it continues	You wrote a PRD (or received one) and want a critique
What you say	"Let me review specs/feature-x.md in mdr before you continue."	"Use mdr to review prd.md and leave comments."
Who comments	You	The agent
How it ends	You click Send & finish	You click End review

1. You review the agent's doc

The common flow right after an agent drafts a document. Tell the agent:

"Let me review docs/specs/feature-x.md in mdr before you continue."

The agent calls mdr_request_review and pauses. mdr opens the file, you highlight text and leave comments, then click Send N comments. The agent receives your feedback as a structured prompt and starts addressing your comments. You can keep sending follow-up batches while it works; Send N & finish sends the last batch and closes the loop. The review is opt-in per request. The agent only pauses when you ask for it. If the agent edits the document before asking you to review it, it calls mdr_baseline first, so the diff shows its changes on the first round.

Automatic before copies. A capable agent calls mdr_baseline on its own, but a smaller or hurried one skips it, and then the diff button is greyed out on the round you most want it. A hook makes it automatic. Add this to ~/.claude/settings.json:

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Edit|Write|MultiEdit",
        "hooks": [{ "type": "command", "command": "mdr baseline --hook --agent Claude" }]
      }
    ]
  }
}

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