Twain
A Markdown viewer that treats .md as a first-class Mac file
Open a Markdown file and read it rendered: GitHub-flavoured tables, task lists, footnotes and alerts, maths, diagrams and highlighted code. Native, offline, and free.
Not shipped yet. The signed, notarised build is in progress; the download and checkout open together when it's ready.
The short version
Twain is a native macOS viewer for the Markdown already on your disk. It renders GitHub Flavoured Markdown faithfully, adds KaTeX maths, Mermaid diagrams and syntax highlighting, and needs no dev server, no account and no network connection. Reading is free, and so are Show Changes and the diagnostics panel.
What the viewer renders
The parts of Markdown a repository actually uses, drawn the way the writer intended.
Fast, faithful rendering Free
An offline remark and rehype pipeline turns Markdown into clean, readable pages with no lag and no dev server to start.
Tables, tasks, footnotes, alerts Free
Full GitHub Flavoured Markdown: tables, task lists, footnotes and the note, tip and warning alert callouts, exactly as your repository writes them.
Syntax highlighting Free
Fenced code is highlighted for dozens of languages, so technical documents stay readable rather than turning into a wall of grey.
KaTeX equations Free
Inline and display maths render through KaTeX, ready for the academic and technical writing that expects it.
Mermaid diagrams Free
Flowcharts, sequence and state diagrams render from fenced blocks as real diagrams, in the app and in the Finder preview.
Outline and table of contents Free
A live outline of every heading lets you jump around a long document instead of scrolling to find your place.
Reading themes and controls Pro
Reading themes plus controls for font and width, so long documents stay comfortable in any light.
No surprise network fetches Free
Remote images in your own files load by default, with a one-tap toggle to block them and a count of what was stopped. In Finder Quick Look, remote subresources are always blocked.
Native, not a web app in a costume
Twain is a SwiftUI Mac app driving an offline rendering pipeline. There is no Electron shell, no account, and no cloud between you and the file. The same renderer draws the app window, the Finder Quick Look preview and the command line output, so what you see never depends on which surface you used.
Documents cannot run code
Markdown from an agent, a colleague or the internet is untrusted input. Twain renders by mapping meaning to safe built-ins and sanitising the result; no script, import or expression inside a document is ever executed. An untrusted file stays inert.
Reading is free
The viewer, Quick Look, maths, diagrams, GFM, Show Changes and diagnostics cost nothing. Pro adds editing, version history, review notes and the agent brief, export, folder mode, reading themes and presentation mode for a one-time price, with a 7-day trial built into the app.
Questions
Does the viewer work offline?
Yes. Rendering is entirely local, nothing in a document is fetched to draw it, and the licence check for Pro also runs on your Mac rather than a server. The app keeps working with no connection at all.
Which Markdown features are supported?
GitHub Flavoured Markdown (tables, task lists, footnotes and alert callouts), KaTeX maths, Mermaid diagrams, syntax highlighting for fenced code, and safe MDX rendering on top.
Is the viewer really free?
Yes. Viewing is free, and so are Quick Look, Show Changes and the diagnostics panel. Pro is a one-time purchase that adds editing, version history, review notes and the agent brief, export, folder mode, reading themes and presentation mode.
What are the requirements?
macOS 14 or later, Apple silicon or Intel.
This page describes what the app does today; when a capability is partial or pending, it says so. See how Twain compares to other Mac Markdown apps.
More capabilities
Try Twain
The free viewer, with a 7-day Pro trial built in.
Not shipped yet. The signed, notarised build is in progress; the download and checkout open together when it's ready.