EventBridge costs when not triggered

If you put a message (below 64k) to EventBridge and no rule is triggered, do you still get charged?

Yes, you are charged for publishing the event to EventBridge, regardless of whether any rule matches the event or not. The cost is based on the number of custom events published. There are no additional charges for rules or event delivery, which means the cost is incurred at the moment of event publication, not based on rule triggering.

If you put a message and it is sent to multiple targets on the same rule, is it billed as one event?

Yes, it is billed as one event for the purpose of event publication to EventBridge. Since there are no additional charges for rules or event delivery to multiple targets, the initial publication of the event is the point of billing. The distribution to multiple targets under a single rule does not incur additional event publication charges.

If you put a message and it triggers multiple rules that send to targets, is it billed as one event?

Yes, in terms of event publication to EventBridge, it is billed as a single event. The act of triggering multiple rules does not affect how the event is billed; the billing is for the event's entry into EventBridge. Because there are no additional charges for rule processing or the delivery of events to the targets specified by these rules, the cost is tied solely to the event's publication, not the number of rules triggered.