1
Download
Grab the free Mac app — Apple Silicon or Intel — and drag it into Applications.
Write with an AI that's on the same page as you.
Margin is Cursor for Prose. Muse, your AI editor, sees exactly what's on the page and follows every change you make. Leave comments and Muse responds right on the page for you to accept, reject or refine.
Chapter One
The lighthouse had been dark for three long years, and no one in the village could say why the keeper had left.
Mara climbed the cliff path anyway, her lantern throwing shapes across the wet rock.
M Muse
Get started
Up and writing in three minutes.
2
Connect your Claude
Have a Claude subscription? Install
Claude Code, run
claude setup-token in a terminal, and paste the token in. Or paste an
OpenRouter or Anthropic API key instead; one OpenRouter key unlocks Claude, ChatGPT,
Kimi, GLM, etc.
3
Write
Make a project, open a page, and say hello to Muse. No account, no sign-up, nothing else to configure.
How it works
An editor on your page,
not a chat window in another tab.
Three ideas make Margin feel less like prompting a bot and more like handing pages to someone who was already reading over your shoulder.
01 — Awareness
It always knows what you just typed.
Muse reads the draft once. After that it tracks what you changed as a diff on every turn — real-time collaboration, not copy-paste. “What do you think of my last pass?” just works, because it knows what you did, not just where the text ended up. And since it isn't re-reading the manuscript every message, it's dramatically cheaper on tokens too.
@@ chapter-one.md @@ - The lighthouse had been dark for years. + The lighthouse had been dark for three + long years, and no one could say why. # Muse sees the delta, not the file.
02 — Control
It proposes. You decide.
Muse can’t touch your words. No agent quietly rewriting the file and leaving you
to wonder what else changed — every edit is a precise red/green proposal drawn on
the exact passage, and nothing else moves. Accept and it applies cleanly.
Reject and it vanishes. Reply to refine, and the revision takes its
place. Or just type inside a proposal to edit it — accept applies
exactly what you see on the page.
…dark for three long years, and no one could say why.
−three long years
+the better part of a decade
03 — Memory
It remembers your world.
Muse keeps its own notes as you write — the characters in your novel, the argument of your essay, the rules you’ve set — plus the craft feedback you’ve given it. Start a fresh chat and it still knows both. Flag chapters, notes, and sources as background reading, or mention any file by name, and it reads them itself: continuity, critique, worldbuilding, across the whole project.
# muse's own notes — .muse/Memory.md - Mara: the keeper's daughter. Fears the sea, climbs anyway. - The light failed three years ago. The village never asked why. # craft feedback you've given - Short declaratives. Cut the adverbs.
Who it's for
Made for the long haul.
Margin earns its keep on work you live inside for weeks, where continuity and voice and revision matter more than a one-shot answer.
Fiction
Muse holds your story bible: characters, timeline, the rules of your world. It flags when a draft drifts from them, suggests lines in your voice rather than some house style, and remembers what you established three chapters ago.
novels · short stories · scriptsNon-fiction
Point Muse at your notes and sources as background reading. It keeps your argument honest across a long manuscript, catches the claim you contradicted forty pages back, and flags where a section needs a citation. It won't rewrite your thinking.
books · essays · reportsBlog posts
Draft fast, then hand it to Muse for the tightening pass: a sharper hook, a killed cliché, a paragraph that finally lands. You see every proposed cut before it happens, so the published voice stays unmistakably yours.
articles · newsletters · docsBut I already paste into a chatbot
Copy-paste is not collaboration.
A chat window forgets your document the moment you close the tab. An AI bolted onto your doc editor sees the paragraph you selected, not the story so far. Both hand back rewrites you have to trust blind or re-merge by hand. Muse lives on the page instead.
chat window
paste, pray, re-merge
- you paste the draft in again, every session — and pay for it in tokens
- it rewrites the whole passage when you wanted one word
- you skim the wall of text wondering what else it changed
- comments, context, and memory vanish when the tab closes
Margin
one shared page
- Muse already knows the draft, your world, and what you just typed
- it proposes a precise red/green edit you accept or reject
- accepted changes apply in place; nothing else moves
- threads, memory, and history persist with the document
Under the hood
Small surface. Careful machinery.
The parts you don’t see are what keep it trustworthy.
Nothing applies without your click
Every Muse edit is a proposal drawn on the live page. Hand-edit the green text and your words become part of it — accept applies exactly what you see, never a version you haven't read. It's never silently applied over your work.
Refine edits in the margin
Comments pin to the exact words, and Muse replies in the thread. Answer a proposal with “shorter, keep the image” and the revision lands in the same thread, replacing the old one. You resolve threads — Muse never quietly closes one on you.
Use any file as Muse context
Flag a file — character sheets, an outline, research notes — as context, and Muse reads it as background at the start of every session. Your worldbuilding stops living only in your head and starts living in the project.
Projects, not just files
Group chapters, notes, and sources into a project, with folders and drag-and-drop — and export it all as clean markdown any time, no lock-in. Mention any file by name mid-conversation and Muse reads it on demand.
No new subscription
Margin is free and runs on your Mac. Sign in with the Claude subscription you already have — or bring any API key and pick your model: Claude, GPT, and more. Download once, keep it forever.
Free · macOS
Work with an editor who remembers.
Margin is free and runs entirely on your Mac, with the Claude subscription you already have — no new subscription to buy. Download once, keep it forever.