Twain
Twain vs Peekdown
Peekdown previews Markdown and MDX in Finder for $3.99. Twain is a review workbench with a free viewer and free Quick Look at its core. The difference is what happens to the components, and what happens after you read.
Not shipped yet. The signed, notarised build is in progress; the download and checkout open together when it's ready.
The short version
For $3.99, Peekdown bundles Quick Look for .md and .mdx, a source editor, annotations that export as AI prompts, and live reload. The differences are two. First, components: Peekdown strips JSX or shows it as code, while Twain renders known components as real UI, labels unknown ones, and never executes anything in the file. Second, the shape of the product: Twain's viewer, Quick Look, rendered diff and diagnostics are free, and a one-time $19 Pro licence adds anchored notes and the agent brief, version history, a block-based visual editor, folder mode and export. Peekdown's annotations are included in its $3.99. If you preview occasionally, Twain's free viewer already covers it. If you review MDX documentation or read a coding agent's output all day, Twain is built for exactly that.
you review MDX documentation and need components rendered rather than stripped, you want anchored notes, a rendered diff and a report an agent can act on, or you are on macOS 14, which Peekdown does not support
you want the cheapest one-time price for Finder previews plus light editing, you live in Obsidian syntax, or you want a single small App Store purchase and nothing else
At a glance
Twain next to Peekdown on the things that decide it. Every fact is dated against Peekdown's public material.
| Twain | Peekdownverified 16 Jul 2026 | |
|---|---|---|
| Price | Free viewer; $19 Pro once, all your Macs (7-day trial) | $3.99 one-time (Mac App Store) |
| Quick Look | MD + MDX | MD + MDX |
| MDX components | Rendered as real UI; unknowns become labelled placeholders | JSX stripped or shown as code |
| Editing | Pro: block-based visual editor, tables edited in place; source for MDX | Source editor with live preview |
| Review notes | Pro: anchored, re-anchoring, resolvable | Annotations export as AI prompts |
| Rendered diff | Against last save, Git HEAD, or any local revision | Not advertised |
| Maths and Mermaid | Both, in the free viewer | Not advertised |
| Export | Pro: PDF, self-contained HTML, print, presentations | Print; copy the file or snippets |
| Folder mode / project search | Pro: open a folder, search across it | Not advertised |
| Obsidian syntax | Not yet; on our gap list | Obsidian-aware: callouts, wikilinks, tags, embeds |
| macOS floor | macOS 14+ | macOS 15+ |
Side by side
What Twain has that Peekdown doesn't
- Semantic MDX. Known components render as real UI, and a component map speaks the names Docusaurus, Mintlify, Nextra and Fumadocs use. Unknown components become labelled placeholders with their props intact. Peekdown strips JSX or displays it as code, which shows the raw source rather than the page a reader would see.
- A free tier that covers the whole reading job. Viewer, Quick Look, maths, Mermaid, and the review tools cost nothing. With Peekdown, $3.99 is the entry point for everything.
- The review loop. Notes anchor to the exact heading or line and survive edits, the rendered diff shows what changed against last save, Git HEAD or any local revision, and the report hands the verdict to a coding agent in one structured block.
- A block-based visual editor (Pro). Peekdown edits source with a preview alongside; Twain edits the rendered page directly, blocks and tables included, and saves back to the file. Folder mode opens a whole directory with project-wide search.
- Maths and diagrams. KaTeX and Mermaid render in the free viewer. Peekdown advertises neither.
- macOS 14 support. Peekdown requires macOS 15, so Sonoma Macs cannot run it at all.
What Peekdown has that Twain doesn't
- Price simplicity. $3.99 once buys the viewer, the editor and the annotation flow. Twain's editor and export sit behind a $19 Pro licence.
- An annotate-to-prompt flow at the centre of the product: notes become structured prompts for an AI assistant.
- Obsidian awareness. Callouts, wikilinks, highlights, tags and embeds are handled.
- Interactive checkboxes in the preview.
- Mac App Store distribution: one-click purchase and automatic updates.
Pricing
Peekdown is $3.99 once from the Mac App Store, and that is the whole bill. Twain splits differently: the viewer, Quick Look and review tools are free, and Pro, a one-time $19 at the launch price rising to $29 after the launch window, adds the editor, export and presentation mode, covering every Mac you own with no device limit, with a 7-day trial and a 14-day money-back guarantee. If your question is 'what does it cost to read rendered Markdown from Finder', Twain's answer is nothing.
MDX
Both apps open .mdx from Quick Look, and that is where the similarity ends. A docs page built from callouts, tabs and steps reads very differently when the components are stripped to plain text or shown as raw JSX. Twain maps known components to real UI, shows unknown ones as tidy labelled placeholders with their props, and parses imports and expressions without ever executing them, so opening a file cannot run project code.
Reviewing with an agent
Peekdown exports annotations as structured prompts for an AI assistant. Twain's loop is wider and lives in one place. The agent opens the file for you with a twain-md:// link, the view live-refreshes as it writes, your notes anchor to the exact spot and survive edits, the rendered diff shows what actually changed, and the report goes back in one block. That loop is free; it is the reason Twain exists.
Questions
Is Peekdown cheaper than Twain?
For the whole product, yes: $3.99 against $19 for Twain Pro. For viewing, no: Twain's viewer, Quick Look, maths, Mermaid and review tools are free, and Peekdown starts at $3.99. You pay Twain only for the editor and export, and Pro has a 7-day free trial before you do.
Don't both support MDX?
Both open .mdx files. Peekdown strips the JSX or displays it as code; Twain renders known components as real UI, labels unknown ones, and executes nothing. If your MDX is prose with the odd tag, the difference is small. If it is a real docs page, it is the whole page.
Which is better for Obsidian notes?
For Obsidian dialect today, Peekdown: it handles callouts, wikilinks, tags and embeds. Twain opens the same files, and Obsidian dialect rendering is on its gap list; this page changes when that closes.
Can I run both?
Yes. macOS shows one app's Quick Look preview per file type: enable the one you want under System Settings, General, Login Items and Extensions, Quick Look. Setting a default app changes what opens on double-click, not what the spacebar shows. Both apps keep working normally when opened directly.
Verification date shown reflects Peekdown's public material as of that day; capabilities and prices can change. Twain facts describe what the app does today; see the full comparison tables and all comparisons. Prices are in USD.
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.