dotPen is a free Markdown viewer for Mac. It renders every file the way it was meant to look, shows what Claude Code, Codex and Cursor just wrote, and marks exactly what changed since you last read it.
Free and open-source Markdown reader for Mac · macOS 15 or later · No account, no tracking
Every session leaves something behind: a plan, a spec, a handoff, a changelog. They pile up across your repos as raw text. And the one thing you need to know, what changed since you last looked, is the hardest thing to see.
Open a plan an agent rewrote and the edits are marked on the page, like a proof: struck words, new lines in green, a tag where lines were cut. Press N to step through them: accept the ones you're happy with, and send the rest back to the agent as a comment. No git, no diff tool, no commit required.
Point dotPen at the folders your agents work in. New files arrive with a green dot, a pencil moves while a file is being written, and the menu bar shows what's happening without opening the app. Open a file mid-write and follow along as each paragraph lands.
Select any line and press C to leave a note in the margin. Send to Agent turns your notes into one prompt with the exact lines they point at, plus what changed. Agents that speak MCP read your comments straight from dotPen and resolve them when the work is done.
When an agent wants your eyes on a plan, it asks dotPen for a review and waits. The file gets an amber dot, your Dock shows how many are waiting, and the page shows the agent's note. Comment on anything you'd change, press Done Reviewing, and the agent picks up your comments and gets back to work.
GitHub Flavored Markdown with tables, footnotes, alerts and task lists. Mermaid diagrams, LaTeX math and highlighted code. Set in New York, SF Pro or SF Mono, at four sizes and three widths, on a white, paper or night page.
Press Space on any .md file in Finder to see it rendered.
Recent files, headings and commands, a few keys away.
Find watched files in Spotlight. Open files and list open tasks from Shortcuts.
Paste a plan into Slack or a doc and keep its shape.
Tick a box and dotPen writes it to the file. It's the only edit dotPen ever makes.
J and K move between files, N between changes, C comments, ⌘U shows the source.
Send a clean PDF, or one self-contained HTML file.
dotpen plan.md opens a file. dotpen ~/code/api watches a folder.
Claude Code, Codex, Cursor, Gemini CLI, and any agent that speaks MCP. One command in Terminal connects an agent to dotPen's local bridge. dotPen also reads Claude Code and Codex session logs, with your permission, to show which agent wrote each file.
No account, no tracking, no analytics. dotPen reads only the folders you choose, keeps your comments in its own container instead of your repos, and the agent bridge listens on your Mac alone.
macOS opens Markdown as plain text. Install dotPen, then double-click any .md file, or select one in Finder and press Space to see it rendered in Quick Look. To make dotPen the default, choose Get Info on a .md file, pick dotPen under Open With, and click Change All.
Yes. dotPen is free and open source, with no account, no ads and no in-app purchases.
Yes. dotPen is a Markdown viewer made for coding agents: it watches the folders where they write, marks new and changed files, and sends your comments back as a prompt. Claude Code, Codex, Gemini CLI and Cursor can also connect to dotPen's local MCP bridge to read and resolve your comments directly.
Only when you tick a task box. Comments, read history and change tracking live in dotPen's own container, so your repos stay exactly as your agents left them.
No. dotPen keeps a copy of each file as you last read it, so it marks changes in files that were never committed.
Yes. An agent connected to dotPen's bridge can ask for your review of a file and wait. dotPen marks the file, shows the agent's note on the page, and when you press Done Reviewing, the agent gets your comments with the exact lines they point at.
Watch your project folder in dotPen. Every plan Claude Code writes shows up in the list with a green dot, rendered with its headings, tasks and diagrams, and the next time it changes, the edits are marked on the page.
A Mac with macOS 15 Sequoia or later.