# Event Handling with Loom
Loom is a system to handle events between applications on the platform.
When a developer registers an application in the Zaikio Hub two list of events can be configured
- events which are fired by the application
- events to which the application wants to subscribe
After an event was fired to Loom, it is verified and then immediately send to all subscribered Apps via HTTP POST to their configured webhook URL.
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# Design Goals
Loom follows an at least once approach. Once an event was received Loom will try hard to deliver this event to each subscriber at least once. To increase reliability senders might want to implement a queue that can buffer events in case of connection issues. Subscribers must be able to handle duplicate messages and implement idempotency.
The order of messages is not guaranteed when pushing to webhooks. Subscribers should not rely on a specific order and need to handle situations in which events arrive out of the band.
The system is scoped by applications. It transfers messages between systems, not between tenants on those systems nor between specific Organizations or Persons.
Loom was designed to handle and delegate events between different applications. Each application can subscribe to any event fired by another application. That means the system should only be used to handle events that might be interesting to other applications. Internal events between different parts of one application (i.e. messages exchanged between internal micro-services) should not be handled with Loom.