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crdt.el is a real-time collaborative editing environment for Emacs using Conflict-free Replicated Data Types.


  • CRDT, darling child of collaborative editing researches…

  • Share multiple buffer in one session

  • See other users' cursor and region

  • Synchronize Org mode folding status

  • Org mode integration

  • Comint derivatives integration (experimental)



crdt.el is now on GNU ELPA! Just M-x package-install crdt.

Start a shared session

A shared session is a place that can contains multiple buffers (or files), and multiple users can join to collaboratively edit those buffers (or files). Think about a meeting room with some people working together on some papers.

In some buffer, M-x crdt-share-buffer. Then enter session name. This add the current buffer to the existing session with that name. If no such exists, it creates a new session with the provided session name, and initially contains the current buffer as a shared buffer.

If a new session is to be created, you need to enter port (default to 6530), optional password and your display name (default to your current (user-full-name)).

Join a session

M-x crdt-connect, then enter address, port, and your display name.

What if we don't have a public IP?

There're various workaround.

  • You can use tuntox to proxy your connection over the Tox protocol. crdt.el has experimental built-in integration for tuntox. To enable it, you need to install tuntox, set up the custom variable crdt-tuntox-executable accordingly (the path to your tuntox binary), and set the custom variable crdt-use-tuntox. Setting it to t make crdt.el always create tuntox proxy for new server sessions, and setting it to 'confirm make crdt.el ask you every time when creating new sessions. After starting a session with tuntox proxy, you can M-x crdt-copy-url to copy a URL recognizable by M-x crdt-connect and share it to your friends. Be aware that according to my experience, tuntox takes significant time to establish a connection (sometimes up to half a minute), however it gets much faster after the connection is established.

  • You can use Teredo to get a public routable IPv6 address. One free software implementation is Miredo. Get it from your favorite package manager or from their website. A typical usage is (run as root)

    # /usr/local/sbin/miredo
    # ifconfig teredo

    The ifconfig command should print the information of your IPv6 address. Now your traffic go through IPv6, and once you start a crdt.el session, your friends should be able to join using the IPv6 address. For more information, see the user guide on the Miredo website.

  • You can use SSH port forwarding if you have a VPS with public IP. Example usage:

    $ ssh -R EXAMPLE.COM:6530: EXAMPLE.COM

    This make your crdt.el session on local port 6530 accessible from EXAMPLE.COM:6530.

    Note that you need to set the following /etc/ssh/sshd_config option on your VPS

    GatewayPorts yes

List active users

In a CRDT shared buffer (either server or client), M-x crdt-list-users.

In the displayed user list, press RET on an entry to goto that user's cursor position. Press f to follow that user, and press f again or M-x crdt-stop-follow to stop following.

List all sessions, and buffer in current session

M-x crdt-list-sessions lists all sessions.

M-x crdt-list-buffers lists all buffers in current session. Or you can also press RET in the session list to see buffers in the selected session.

Stop sharing

M-x crdt-stop-session stops a session you've started and disconnect all other users from it. This will ask for your confirmation, customize crdt-confirm-stop-session if you want to disable it.

You can also press k in the session list (show it by M-x crdt-list-sessions).

M-x crdt-stop-share-buffer removes current buffer from its CRDT session (this operation is only allowed at server side). Or press k in the buffer list.

Disconnect from a session

M-x crdt-disconnect, then choose a session to disconnect from.

You can also press k in the session list (show it by M-x crdt-list-sessions).

The server Emacs has the privilege to disconnect a user from a session. To do so, press k on an entry in the user list (show it by M-x crdt-list-users).

Visualizing author of parts of the document

Turn on crdt-visualize-author-mode. Colored underlines are added to each part of the document, based on which user authored it.

Synchronizing Org folding status

Turn on crdt-org-sync-overlay-mode. All peers that have this enabled have their folding status synchronized. Peers without enabling this minor mode are unaffected.

Comint integration

Just go ahead and share you comint REPL buffer! Tested: shell and cmuscheme. By default, when sharing a comint buffer, crdt.el temporarily reset input history (as in M-n M-p) so others don't spy into your .bash_history and alike. You can customize this behavior using variable crdt-comint-share-input-history.