You can use free Actions that have triggers and reactions only in response to certain events. Each such reaction and free action lists the trigger that must happen for you to perform it. When its trigger is satisfied—and only when it is satisfied—you can use the reaction or free action, though you don’t have to use the action if you don’t want to.

There are only a few basic reactions and free Actions that all characters can use. You’re more likely to gain Actions with triggers from your class, feats, and magic items.

Limitations on Triggers

The triggers listed in the stat blocks of reactions and some free Actions limit when you can use those Actions. You can use only one action in response to a given trigger. For example, if you had a reaction and a free action that both had a trigger of “your turn begins,” you could use either of them at the start of your turn—but not both. If two triggers are similar, but not identical, the GM determines whether you can use one action in response to each or whether they’re effectively the same thing. Usually, this decision will be based on what’s happening in the narrative.

This limitation of one action per trigger is per creature; more than one creature can use a reaction or free action in response to a given trigger. If multiple Actions would be occurring at the same time, and it’s unclear in what order they happen, the GM determines the order based on the narrative.