When developing applications, you often would like to off-load some common task to some existing service provider. It could be handling payments or sending emails. In addition, sometimes your application might have more complex validation rules than Reindex provides and you’d need to write a small custom backend to handle that.
Reindex provides hooks as a mechanism to integrate third-party services and backends. It allows you to specify a URL to send a POST request to in response to a certain mutation for a certain type.