Folio

Folio is a local-first desktop print preview for Markdown. Open a document, choose its style, preview physical pages, then print or save a PDF.

Current status: macOS alpha (0.1.0). Download the universal Apple Silicon and Intel installer from 0.1.0 alpha, or build from source. It is ad-hoc signed, without Developer ID signing or notarization. Intel runtime testing and other release checks remain outstanding.

Features

• Open .md and .markdown files using the file picker, Finder Open With, recent files, or drag and drop.
• Reload documents when an external editor saves them, including saves that replace the file.
• Render tables, highlighted code, Mermaid diagrams, math, and local raster images.
• Choose document themes, typography, margins, A4 or Letter paper, and portrait or landscape orientation.
• Split long text, lists, code, and tables across pages, with repeated table headers.
• Print or save a PDF through the native macOS print dialog.

Folio previews files edited in another application. Local documents stay on your device.

Install and use

If you have a built alpha DMG, quit Folio, open the DMG, and drag Folio into Applications. Choose Replace to update an existing installation. Keep the previous DMG for rollback.

1. Open a Markdown file from Folio or use Finder's Open With → Folio. Double-clicking opens Folio only when it is the file's associated app.
2. Adjust the document settings and inspect the preview.
3. Choose Print, or choose Export PDF and use the print dialog's Save as PDF destination.

Keyboard shortcuts

Action	macOS shortcut
Open file	⌘O
Print	⌘P
Export PDF	⇧⌘E
Toggle settings	⌘,
Zoom in / out	⌘+ / ⌘−
Reset zoom	⌘0

Development

Prerequisites:

• Node.js 20+ and pnpm 10+; the alpha workflow uses Node.js 22.
• Rust stable and the Tauri 2 platform prerequisites.
• macOS for building and testing this alpha.

pnpm install --frozen-lockfile
pnpm tauri dev

For a browser-only development preview, run pnpm dev and open the local URL it prints, normally http://localhost:1420. Do not open index.html directly. Browser file picking works, but native paths, recent-file reopening, file watching, relative filesystem images, and printing require the desktop app.

The marketing landing page is available at http://localhost:1420/landing.html. It has a separate entry point and stylesheet; the desktop app still opens at /. Both entry points are included in pnpm build.

Checks

pnpm check
pnpm rust:fmt
pnpm rust:clippy
pnpm rust:test

pnpm check runs lint, formatting, frontend tests, TypeScript checks, and the production frontend build. Open the kitchen-sink fixture in the packaged app to check rendering and native PDF output.

Build the macOS installer

rustup target add aarch64-apple-darwin x86_64-apple-darwin
pnpm build:alpha

The universal DMG is written to src-tauri/target/universal-apple-darwin/release/bundle/dmg/. The build uses ad-hoc signing; no Apple signing credentials are required.

Architecture

• src/document owns rendering, pagination, print styling, diagrams, highlighting, and themes.
• src/features/files owns the native/local file boundary.
• src/features/settings owns the document inspector.
• src/stores contains document state and persisted settings.
• src-tauri validates Markdown paths, reads files, watches external changes, and handles native file-open events and launch arguments.

Document themes map typed definitions to scoped CSS variables. Raw HTML is sanitized, Markdown scripts are not executed, and Mermaid uses strict security mode.

Limitations

• This is an experimental macOS alpha. Windows and Linux releases are not validated.
• Intel hardware execution, physical drag-and-drop, physical printing, clean-Mac downloaded installation, and the GitHub alpha workflow remain unverified.
• Content that cannot fit a page shows a layout warning and blocks print/export. Full unpaginated content remains available for inspection.
• Unusual custom CSS needs checking in the exported PDF.
• Remote images are blocked. Native local images support PNG, JPEG, GIF, and WebP inside the document directory; SVG file images are unsupported.
• PDF export uses the native print dialog; one-click PDF saving is not implemented.
• Updates require manually replacing the app. There is no automatic updater.

License

Folio is available under the MIT License.