Collaboration

Collaboration runs on the same sync server and the same websocket. Set collab on the sync prop:

import { MdxEditor } from "@fumadocs-editor/ui";

export function CollabEditor({ path, name }: { path: string; name: string }) {
  return <MdxEditor sync={{ path, collab: { user: { name, color: "#7c3aed" } } }} />;
}

user is the presence identity shown at your caret on other screens. collab: true joins as a guest. Yjs is loaded lazily, so editors that never enable collab never download it.

How it works

With collab on, the server owns the file:

• Every open file has one shared document on the server, and the server is the only writer to disk. Blocks nobody touched still serialize byte-for-byte.
• Changes on disk (a git pull mid-session) merge into the shared document. When the same block changed on both sides, the editor wins and the disk is rewritten. There is no conflict chip: the document is shared, so there is no local side to keep.
• When the last client leaves, the server flushes and drops the document after evictAfterMs (60 s by default).

What changes

Presence carets show each peer's name. A server auth scope with a user overrides whatever name a client claims. Plain sync tabs and collab tabs can edit the same file: a sync write reaches the server's document like any other disk change.

Restarts

There is no persistence beyond the file. A server restart, or eviction followed by a reopen, re-seeds the document from disk, and clients holding older state rebuild from the server. Two windows where edits can be lost:

• A hard kill can lose edits still inside the save debounce (under a second). An orderly shutdown flushes.
• Edits typed while the server was down are discarded by the reset. Edits made while merely disconnected (server up, network down) are buffered and converge on reconnect.

Your own session

createCollabSession from @fumadocs-editor/core/collab is the collab counterpart of createFileSession: it returns the shared document and awareness for a shell that is not React.