Markdown Editor Pro

A single-file, zero-install Markdown editor. Open a folder, hit Ctrl+S, and the file on disk is updated — no download dance.

Start writing →

The dark theme in action: Markdown source with line numbers on the left; on the right, a live preview showing a YAML front matter card, the heading, three status badges, a callout and a bulleted list — Write on the left, see it on the right — scroll position and styling follow along.

Real file system integration — save in place through the File System Access API, no download-and-replace
Side-by-side dual preview — the left pane follows your buffer, the right pane holds any other .md file for reference, with optional synced scrolling
Three tuned themes — dark, light, and warm sepia, with the preview styled to match
Interface in three languages — Traditional Chinese, English, and Japanese, switched from the pill in the top-right corner
YAML front matter rendered as a card rather than broken markdown
Your files never leave your machine — no backend, no upload, no account

Dual preview: two documents side by side

The left pane follows the file you are editing; the right pane loads any other .md independently. Where it really earns its keep is proofreading — put a translation next to its source, tick synchronised scrolling, and both panes stay on the same paragraph.

Dual preview used for proofreading: the English source Template.md on the left, the Chinese translation Template_cn.md on the right, with the front matter cards, headings, badges and lists lining up section by section, and synchronised scrolling switched on — Source on the left, translation on the right — synchronised scrolling keeps both on the same paragraph.

Three themes, preview included

A theme is not just the editor's background colour. The toolbar, sidebar, preview, code blocks, blockquotes, tables and the YAML front matter card all read from the same set of CSS variables, so you never end up half-switched with a bright editor next to a dark preview.

Light theme: the same document with a white preview pane — front matter card, badges, callout and inline code all stay legible at high contrast — Light: white and high-contrast, made for daylight and projectors

Warm theme: the same document on a paper-like sepia background, with the front matter card, heading, callout and list all in the same warm palette — Warm: paper-like sepia, the easiest on the eyes for long reading and proofing

Your choice is remembered in the browser, so the next visit opens in the theme you left. The same goes for the interface language and for whether the sidebar and editor pane are open.

How it compares

What matters	This editor	Desktop apps	Typical online editors
Needs installing	No	Yes	No
Overwrites the original file on disk	Yes (Chromium)	Yes	Usually not — download, or link a cloud drive
Needs an account	No	Usually not	Often
Are your files uploaded	No, there is no backend	No	Depends on the service
Dual preview (a second file open for reference)	Built in	Rare	Rare
Price	Free	Free through one-off purchase	Free or subscription
Plugins and ecosystem	None	Rich	Few

That last row is the honest one: if you need plugins, graph views or backlinks, a desktop app is still the better tool. This editor solves a different problem — open a browser and edit the .md that is already on your disk, leaving nothing installed behind.

Five minutes to learn all of it

The manual is five chapters, from opening a folder to why only Chromium browsers can write to your disk. Every chapter can be downloaded as a .md file — drop it back into the editor and you have a ready-made sample document.

The full experience — opening a folder and saving in place — needs a Chromium-based browser: Chrome, Edge, Brave, or Arc. Firefox and Safari can edit and preview, but fall back to a download. The reason is in why only Chromium browsers can save straight to disk.