Cowrite
A shared Markdown document you and anyone else can edit at the same time. Send the link, watch each other's cursors, and see edits appear as they're typed. No sign-up, nothing stored.
How it works
Real-time collaboration sounds simple until two people type in the exact same place at the same time. Cowrite handles that with a CRDT, a conflict-free replicated data type. Every character each person inserts or deletes carries enough identity that all the edits can be merged in any order and every browser lands on exactly the same document, with nothing lost and no "someone else is editing" lock. Under the hood it's the Yjs library. Your keystrokes are turned into tiny binary updates, relayed to everyone else in the room over a realtime channel, and applied instantly. The relay only ever sees those opaque edit deltas, never a stored copy of your document.
Write in Markdown, see it live
You type Markdown on the left and get a rendered preview on the right that updates as anyone in the room types. Headings, lists, tables, code blocks, quotes, and links all work. The preview is sanitized before it's shown, so a shared document can't be used to slip a script into anyone's browser. On a phone the two panels become tabs so you can flip between writing and reading.
No account, nothing stored
There's no sign-up, no email, and no database. A document exists only in the browsers of the people currently in it. That means it's private and instant, and it also means the note is meant to be live rather than permanent: keep the tab open while you work, and copy the text out when you're done. Want a fresh, empty document? Hit "New document" for a brand-new private link.
Do I need an account?
No sign-up and no login. Open the page, share the link, and start writing together right away.
How does it avoid conflicts?
It uses a CRDT (via Yjs). Every person's keystrokes are merged deterministically, so two people can type in the same spot at once and nothing is overwritten.
Is my document stored anywhere?
No. The document only lives in the browsers of the people currently in the room. The server just relays edits between them. When everyone leaves, it's gone.
Can I write Markdown?
Yes. You write Markdown on the left and see a safe, live HTML preview on the right, updated as everyone types.
How many people can join?
Several people can edit at the same time. You'll see everyone's presence and where their cursor is.
I build tools like this every day.
Senior full-stack engineer, available for senior or contract work, fully remote. See the rest of the lab or get in touch.