Write calmly, on folded paper
Source and finished page live on the same sheet, so what you type is already how it will look.
The machine below is Folding Mirror itself, not a recording. Type on the paper, then move the caret onto any line — that line turns back into source.
No download. Just write two lines.
Live preview isn't a preview pane pinned beside your text. There is no preview step at all.
# Autumn notes What you put on paper rarely means the same thing when you read it a day later. ## One — the light At four in the afternoon the light cuts the desk in two: **the bright half** falls on the page, and the dark half is left to *the paragraphs I haven’t worked out yet*. > Put the sentence that matters first. ### Two rules - Mornings: write, never revise - Evenings: revise, never write ```js const light = today.at(16) ``` | Time | Doing | Minutes | | --- | --- | ---: | | Morning | writing | 90 | | Evening | revising | 45 | - [x] Finish the draft - [ ] Read it again after a night When it goes on from here, follow the frame in [[Writing/Long-form outline]].
- Mornings: write, never revise — 25 minutes on a timer
- Evenings: revise, never write — read it aloud first
- Sleep on it before it is final — nothing goes out at night
- ### Two rules+ ### Three rules- - Mornings: write, never revise+ - Mornings: write, never revise — 25 min⋯ 4 more changes
↑ ↓ move the caret to see inline sourceAa / ◫ switch live preview and split viewtry typing ## Heading **bold
What you type is the page
The marks stay behind the words. Only the line your caret is on shows its source; everywhere else stays set.
Your files stay yours
One ordinary folder, a pile of plain .md. Close Folding Mirror and every other editor still opens them.
An assistant you call for
The AI takes no space until you want it, and it lays out every edit for you before it touches the file.
Everything a long piece needs, all of it done on the same sheet — without leaving the window or opening a second one.
What it does
Live preview
Aa / ◫Marks fade behind the words; only the line your caret is on shows its source. A split view is there when you want it.
Focus & typewriter
F8 F9Dim everything but the paragraph you are in, and pin the current line at a fixed height.
Tabs
⌘ TSeveral documents in one window, so moving between them never costs you your place.
Formulas
$…$Inline and display maths through KaTeX. It renders once your caret leaves the pair.
Tables
| … |Real tables you edit in place — not a dialog, and not a read-only picture.
Mermaid
```mermaidFlowcharts, sequence and Gantt diagrams, either in a fence or as their own .mmd file.
Drawings
.excalidrawAn Excalidraw canvas embedded in the page. Drag its corner to resize it right there.
Links & mentions
[[ ]]Join two notes with square brackets and the backlinks grow on their own.
Outline & search
⌃ ⌘ 1Navigate a long piece by its headings; find anything across the library by its text.
Checkpoints
⌘ ⇧ HEvery edit has a way back — including taking the whole library to an earlier moment.
Export
PDF / HTMLExport with a CJK font subset embedded, so a PDF never comes out full of empty boxes.
Images and files
Drag one in and the file lands beside the document — nothing uploaded, re-hosted or renamed.
Long pieces go wrong in different ways. These four are the ones Folding Mirror was built around.
See if one of these is you
Writing a paper
Formulas are a row of $ while you write, a diagram means opening a second app, and by the third draft the paragraph you liked in the first one is gone.
Formulas set themselves where they sit, diagrams and canvases grow inside the text, and the library can go back to any earlier moment.
Writing technical docs
The diagram lives in another tool and comes back as an image. Change the architecture and it quietly stops matching the words — and nobody can tell which picture went stale.
The diagram is a mermaid block in the document: edit a line and it redraws, and it travels along with the PDF and HTML exports.
Keeping notes for years
Notes go into an app, and years later getting them out means an export in a private format that you cannot read either.
A plain folder of plain .md. Backlinks and full-text search are there all the same, and uninstalling costs you nothing.
Handing the piece over
It looks right in the editor and falls apart everywhere else — a PDF of empty boxes where the CJK glyphs should be, or HTML that lost its styling on the way out.
Exports embed a font subset, so the PDF reads like the screen did; the HTML carries its styling with it.
This section is the back of the sheet. Here the AI is an assistant you call for, not a second author sitting in the room.
An assistant you call for
Your key, your account. Nothing is proxied, held for you, or copied on the way through.
- Bring your own key
- Over twenty providers are preset — Anthropic, OpenAI, DeepSeek, Moonshot, Zhipu — and any compatible endpoint can be typed in. Keys are kept in the system keychain and never leave the machine.
- Edits go through you
- Before the assistant touches a document you get a card: what it adds, what it removes, line by line. It only reaches disk once you approve.
- Say it and the app does it
- “Turn on focus mode.” “One size bigger.” “Open my November note.” It reaches for the menu so you don't have to — and since those changes happen in front of you, they need no approval.
- Skills and MCP
- A built-in skills folder, plus any standard MCP server. Looking things up, running a script, reaching your own tools — all from the one panel.
- Context you can see
- How much of the window is used, and what this turn cost — the indicator is always there. No guessing, no silent truncation.
Nothing of yours is held here
- Local firstEvery document sits in your own folder; reading and writing are things this machine does.
- No accountInstall and write. No sign-up, no login, no subscription wall.
- Plain .mdNo proprietary format, no database. Uninstall it and every file is still there.
How is this different from other Markdown editors?+
Most land on one of two sides: a quiet tool for writing a single document, with versions, the library and publishing all left outside the window — or a knowledge base that holds a whole library while the screen you actually write on is still source beside preview. Folding Mirror folds those two halves onto one sheet. Tables you edit in place, formulas, Mermaid and an Excalidraw canvas all live in the text itself rather than in a dialog, while the library behind them has checkpoints, backlinks and full-text search — plus an assistant whose edits go through an approval card first, built-in MCP, and exports that embed a CJK font subset. Underneath is always plain .md in a folder you chose: no account, no database.
Where are my files kept?+
In any folder you choose. Nothing is imported, moved or indexed into a database — what you see is the .md file on disk. Attachments sit next to the document; drawings go in drawings/.
Does it need the internet? Are my documents uploaded?+
Writing works entirely offline. The only time it goes online is when you call the AI assistant, and then your machine talks straight to the provider whose key you entered. Nothing is relayed through us and no copy is kept. Skip the AI and Folding Mirror never sends a byte.
Is the AI an extra subscription?+
No. Folding Mirror does not charge for AI and does not resell credits. You bring your own API key, and usage is settled between you and your provider. Around twenty providers are preset — Anthropic, OpenAI, DeepSeek, and others — so a key is all it takes.
Which systems does it run on?+
macOS 12 and later today, with separate builds for Apple silicon and Intel. Windows and Linux are planned, but not scheduled.
How much does it cost?+
A one-time purchase — buy it once, keep it. Not a subscription. $25.90, or $14 for the first 40 days after launch; one key covers 3 machines and a year of updates, and it keeps working after that year whether or not you renew. The pricing page has the details; the release date does not have one yet.
The installers are served from this site; the checksums are produced by the build.