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Installation

Requirements​

  • macOS 14 (Sonoma) or later
  • Apple Silicon or Intel processor

Twain ships as a single universal app that runs natively on both architectures.

Twain comes in two editions: a direct download (a notarised .dmg from twain.md) and the Mac App Store. They render identically and open the same documents; a few sandbox-related features differ. The direct download is the edition that has shipped, and this page covers it. The Mac App Store edition has not been released yet; when it is, it will install and update through the store like any other app.

Install the app​

  1. Download Twain from twain.md and open the disk image.
  2. Drag Twain into your Applications folder.
  3. Open it from Applications (or Launchpad) the first time.
Keep it in /Applications

Move Twain into /Applications rather than running it from Downloads. Twain's Quick Look preview extension only activates when the app lives there. Double-clicking works wherever Twain is installed, once it is the default handler. See Quick Look previews.

Make Twain your default viewer​

macOS decides which app opens a Markdown file, and which app draws its Finder preview, from the default application for that file type. To make Twain that app:

  • Choose Twain ▸ Set as Default Markdown Viewer… from the menu bar, or
  • Click Make Default on the welcome screen.

Twain claims the Markdown and MDX types (.md, .markdown, .mdown, .mkd, .mkdn, and .mdx). It deliberately does not take over generic plain-text files, so it will not become the handler for every .txt on your Mac.

Once Twain is the default, pressing the spacebar on a Markdown file in Finder shows a Twain preview, and double-clicking opens it in the app.

First launch​

What the app sends on first launch

Twain is currently version 1.0.0, signed with a Developer ID and notarised by Apple, so it opens without a Gatekeeper warning. Rendering is entirely offline, and no document you open is ever sent anywhere. The direct download does send one small anonymous check-in to twain.md at three moments (app launch, starting the trial, and activating a licence). It reports only the app version, and on launch which edition is running (free, trial, or licensed); on activation it also sends a one-way fingerprint of the licence key, so we can count how many Macs a licence runs on. It never includes your name, email, a device identifier, or anything about your documents, and Twain never reads the response back. Turn it off under Twain ▸ Settings ▸ Privacy. The Mac App Store edition sends no check-in at all.

After the first launch you will see the welcome screen with buttons to open a file or a folder, a list of recent documents, and, if Twain is not yet your default viewer, a prompt to make it so. Opening a single file is free; Open a Folder… is a Pro feature, so on a free install it shows the Unlock Pro sheet rather than a folder chooser.

Updates​

The direct download checks for updates in the background and tells you when one is available. Nothing is ever downloaded and installed on its own: every update waits for you to accept it. You can also check on demand with Twain ▸ Check for Updates…. The Mac App Store edition updates through the App Store instead. See Software updates and Editions.