# Modules

Synapse supports extending its functionality by configuring external modules.

Note: When using third-party modules, you effectively allow someone else to run custom code on your Synapse homeserver. Server admins are encouraged to verify the provenance of the modules they use on their homeserver and make sure the modules aren't running malicious code on their instance.

## Using modules

To use a module on Synapse, add it to the `modules` section of the configuration file:

    modules:
      - module: my_super_module.MySuperClass
        config:
          do_thing: true
      - module: my_other_super_module.SomeClass
        config: {}

Each module is defined by a path to a Python class as well as a configuration. This information for a given module should be available in the module's own documentation.

## Using multiple modules

The order in which modules are listed in this section is important. When processing an action that can be handled by several modules, Synapse will always prioritise the module that appears first (i.e. is the highest in the list). This means:

- If several modules register the same callback, the callback registered by the module that appears first is used.
- If several modules try to register a handler for the same HTTP path, only the handler registered by the module that appears first is used. Handlers registered by the other module(s) are ignored and Synapse will log a warning message about them.

Note that Synapse doesn't allow multiple modules implementing authentication checkers via the password auth provider feature for the same login type with different fields. If this happens, Synapse will refuse to start.

## Current status

We are currently in the process of migrating module interfaces to this system. While some interfaces might be compatible with it, others still require configuring modules in another part of Synapse's configuration file.

Currently, only the following pre-existing interfaces are compatible with this new system:

- spam checker
- third-party rules
- presence router
- password auth providers