Edit markdown.
Nothing else.
Three panes. File browser on the left, editor in the middle, live preview on the right. No plugins, no cloud sync, no collaboration features, no subscription. Just a fast, focused editor for people who live in markdown and want their tools to stay out of the way.
Your files are markdown on disk. Open them with anything, anywhere, forever.
The Problem
Every markdown editor wants to be something else.
Some want to be Notion. Some want to be a knowledge graph. Some want your files in their cloud. Most want a subscription. The ones that don't want any of that are either abandoned, buggy, or buried under features you'll never use.
This editor does one thing: lets you open markdown files on your computer, edit them with syntax highlighting and a live preview, find them easily in a file browser, and get out of your way. That's it. That's the feature list.
Features
The short list. Deliberately.
Three-Pane Layout
File browser on the left, CodeMirror editor in the middle, live GitHub Flavored Markdown preview on the right. Bidirectional scroll sync keeps them aligned. Everything visible at once.
File Browser
Expandable directory tree with auto-refresh on file system changes. Double-click folders to set as root. Right-click for new files, new folders, rename, delete, or "Show in Finder." Only markdown files are clickable — no noise.
Session Restore
Close the app, open it tomorrow — all your tabs are still there, your active file is still selected, your folder is still set. Windows remember their size and position. Pick up exactly where you left off.
Smart Formatting Toolbar
Bold, italic, headings, lists, blockquotes, code blocks, links, images, horizontal rules. Buttons detect if formatting is already applied and toggle it off. Heading buttons cycle through levels. List buttons work on multi-line selections.
Search & Replace
Cmd+F to find, Cmd+H to replace. Case sensitivity toggle, match count, and navigation between results. Built into CodeMirror — fast and reliable on any file size.
External Change Detection
Edit a file in another app while it's open here — you get a diff view showing exactly what changed, with options to keep your version, accept the external changes, or save as a new file. No silent overwrites.
And Also
The things you'd expect to work, working.
Open multiple files. Unsaved changes show a dot. Close buttons on each tab. New tab button for untitled documents.
GitHub Flavored Markdown rendered in real time. Local and remote images display inline. Scroll sync snaps to top.
Dark, light, or system. Seven accent colors. Configurable editor and preview fonts from your system font library.
Cmd+Shift+N for a new window. Each window preserves its own tabs and folder. All windows restore on relaunch.
Registers as a handler for .md, .markdown, .mdx, .txt, and more. Shows up in Finder's "Open With" menu.
Checks for new versions automatically. Downloads in the background. One-click "Restart & Install" when ready.
External Change Detection
Edit it somewhere else. Nothing gets lost.
Open a file here, edit it in another app — the editor detects the change and shows you a full diff view. Keep your version, accept the external changes, or save as a new file. No silent overwrites.
Settings
Theme, accent color, editor font, preview font, font size, line numbers
Under the Hood
Security-hardened. Not an afterthought.
XSS prevention
DOMPurify sanitizes all rendered markdown before it hits the preview pane. No script injection through crafted markdown files.
Sandboxed windows
Chromium sandbox enabled. Context isolation enforced. All file operations route through IPC handlers with path validation.
Filesystem access control
Path validation limits access to home directory and volumes. Sensitive directories (.ssh, .gnupg, .aws) are blocked. No path traversal.
Signed & notarized
Code signed with Apple Developer ID. Notarized with Apple's notary service. No Gatekeeper warnings on first launch.
No telemetry
No analytics. No crash reporting. No network calls except update checks to GitHub Releases. Your writing stays on your machine.
Open source (MIT)
Full source on GitHub. Adversarial security review completed at v0.1.11. Every line is auditable.
What It Doesn't Do
The features I left out on purpose.
No cloud sync. No collaboration. No plugin system. No Vim mode. No WYSIWYG. No proprietary file format. No account creation. No subscription.
Every markdown editor eventually tries to become a knowledge management platform. This one won't. The file system is your organizational layer. Markdown is your format. This app just makes editing those files fast and pleasant.
Who It's For
People who already know they want a markdown editor.
Developers, writers, and note-takers who live in markdown daily. People who maintain README files, blog posts, documentation, meeting notes, or personal knowledge bases — and want an editor that opens fast, renders cleanly, and doesn't ask them to create an account or install twelve plugins to get basic functionality.
If you've ever opened a markdown editor and thought "I just want to edit the file" — this is the answer to that.
Technical Stack
Support & Contributions
Found a bug? Have an idea?
Simple Markdown Editor is open source and actively maintained. If something isn't working or you've hit a workflow gap, open an issue.
Try it. It's free.
Open source, no sign-up, no telemetry. Download the latest release and start editing.