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We need a better Markdown previewer.


pen is a Markdown previewer written in JavaScript, aiming to just work.

There are literally tons of Markdown previewers out there. I love some of them, I even made one of them. Nevertheless, we always need a better one, don't we?

Using pen is super simple, we don't need to install any special editor or launch any GUI application. pen is just a tidy command-line tool. You can use your favourite editor and browser. No manual refresh is even needed.

Also, the previewer renders the content using React. It means that it will not re-render entire DOM when the document is updated. This is a huge advantage because images or other media won't be reloaded for the DOM update.

I personally love to use pen, and I hope you love it too. ✒️


Here is a short demo showing how awesome pen is.


The following demo shows pen incrementally updates only modified part using React and its Reconciliation.

incremental update


pen uses Node.js >= 4.0. It may not work on earlier versions.


Using npm:

npm i -g pen

You can try using pen with npx:

npx pen


To use pen, simply run the pen command.


The command above will launch a pen server and open the file in your default browser. The server will listen to a 6060 port by default. To be honest, you don't even need to launch it with a filename. You can manually open http://localhost:6060/, or any other files in the same directory.

To stop the server, enter ^C.

For the further details of the pen command, please enter pen -h or pen --help.


Pen uses markdown-it as Markdown parser by default, but it also supports Pandoc. Please provide a proper Pandoc format for the value.

pen --pandoc gfm


I welcome every contribution on pen. You may start from forking and cloning this repo.

git clone
cd pen

# Install dependencies
npm i

# Lint, build, and test pen codes at once
npm test

To build frontend scripts:

npm run build

To lint with ESLint:

npm run lint

To test with Mocha

npm run mocha


Pen is released under the MIT License.