depot/nixos/modules/services/matrix/mjolnir.md

Mjolnir (Matrix Moderation Tool)

This chapter will show you how to set up your own, self-hosted Mjolnir instance.

As an all-in-one moderation tool, it can protect your server from malicious invites, spam messages, and whatever else you don't want. In addition to server-level protection, Mjolnir is great for communities wanting to protect their rooms without having to use their personal accounts for moderation.

The bot by default includes support for bans, redactions, anti-spam, server ACLs, room directory changes, room alias transfers, account deactivation, room shutdown, and more.

See the README page and the Moderator's guide for additional instructions on how to setup and use Mjolnir.

For additional settings see the default configuration.

Mjolnir Setup

First create a new Room which will be used as a management room for Mjolnir. In this room, Mjolnir will log possible errors and debugging information. You'll need to set this Room-ID in services.mjolnir.managementRoom.

Next, create a new user for Mjolnir on your homeserver, if not present already.

The Mjolnir Matrix user expects to be free of any rate limiting. See Synapse #6286 for an example on how to achieve this.

If you want Mjolnir to be able to deactivate users, move room aliases, shutdown rooms, etc. you'll need to make the Mjolnir user a Matrix server admin.

Now invite the Mjolnir user to the management room.

It is recommended to use Pantalaimon, so your management room can be encrypted. This also applies if you are looking to moderate an encrypted room.

To enable the Pantalaimon E2E Proxy for mjolnir, enable services.mjolnir.pantalaimon. This will autoconfigure a new Pantalaimon instance, which will connect to the homeserver set in services.mjolnir.homeserverUrl and Mjolnir itself will be configured to connect to the new Pantalaimon instance.

{
  services.mjolnir = {
    enable = true;
    homeserverUrl = "https://matrix.domain.tld";
    pantalaimon = {
       enable = true;
       username = "mjolnir";
       passwordFile = "/run/secrets/mjolnir-password";
    };
    protectedRooms = [
      "https://matrix.to/#/!xxx:domain.tld"
    ];
    managementRoom = "!yyy:domain.tld";
  };
}

Element Matrix Services (EMS)

If you are using a managed "Element Matrix Services (EMS)" server, you will need to consent to the terms and conditions. Upon startup, an error log entry with a URL to the consent page will be generated.

Synapse Antispam Module

A Synapse module is also available to apply the same rulesets the bot uses across an entire homeserver.

To use the Antispam Module, add matrix-synapse-plugins.matrix-synapse-mjolnir-antispam to the Synapse plugin list and enable the mjolnir.Module module.

{
  services.matrix-synapse = {
    plugins = with pkgs; [
      matrix-synapse-plugins.matrix-synapse-mjolnir-antispam
    ];
    extraConfig = ''
      modules:
        - module: mjolnir.Module
          config:
            # Prevent servers/users in the ban lists from inviting users on this
            # server to rooms. Default true.
            block_invites: true
            # Flag messages sent by servers/users in the ban lists as spam. Currently
            # this means that spammy messages will appear as empty to users. Default
            # false.
            block_messages: false
            # Remove users from the user directory search by filtering matrix IDs and
            # display names by the entries in the user ban list. Default false.
            block_usernames: false
            # The room IDs of the ban lists to honour. Unlike other parts of Mjolnir,
            # this list cannot be room aliases or permalinks. This server is expected
            # to already be joined to the room - Mjolnir will not automatically join
            # these rooms.
            ban_lists:
              - "!roomid:example.org"
    '';
  };
}