Timing of Bonus Actions

[JonBeowulf]

I'm not looking for a debate on when certain bonus actions can be taken. I'd like to put together an exhaustive list of how the timing of bonus actions are described so I can (attempt) to clear things up in Session 0. I've found easy ones...

Things that can happen whenever you want on your turn
- during your turn, you can Y as a bonus action
- as a bonus action on your turn, you can Y
- you can Y on your turn as a bonus action
- other similar examples

Things that happen after after an action on your turn
- after you X, you can Y as a bonus action

Things that happen while an action is being performed
- while you X, you can Y as a bonus action

Things that happen during an ongoing effect
- while X is in effect, you can Y as a bonus action

And I've found complicated/confusing ones...
Things with a timing that requires judgment based on the requisite action (Sage Advice and DM Rulings are all over these) I typically rule that these can be after, during, or before the action (but lock the character into that action).
- when you use your action to X, you can Y as a bonus action
- if you take the X action on your turn, you can Y as a bonus action
- when you take the X action on your turn, you can Y as a bonus action

Are there other phrases used to describe the timing of bonus actions?

[Zhorn]

I think you've got all the important frameworks listed here. Short of parsing every single bonus action for the slightest wording variations I think you have it all covered.
Good work on collecting these. I think I'm going to have to make a copy of this list for my DM notes now also, as it is a good idea to have a general mention of these before players start on character builds that may require an agreed understanding of bonus actions.

Especially with the likes of
- when you use your action to X, you can Y as a bonus action
- if you take the X action on your turn, you can Y as a bonus action
- when you take the X action on your turn, you can Y as a bonus action
Which I'd have just grouped under the single

- after you X, you can Y as a bonus actionbut yeah, not everyone is going to share that opinion. (just making conversation, not attempting to start a debate on that.)

[Segev]

There is always a risk of an action becoming invalid by negating its trigger if you permit an action to be taken before you take its permitting action. Still, this is a matter for a DM to rule on, so ask yourself if the described action of the character makes sense to permit the bonus action before the action granting permission to use said bonus action. If it is guaranteed that the requisite action will be taken and the mover described by the player make sense narratively, I suggest permitting the actions in any order the player wants.

[JonBeowulf]

Yes, I agree. Those are always case-by-base. Some are no-risk to lose the triggering action (like the popular "shield bash to knock prone" BA), but any damage-doing BA that is triggered by making an attack or casting a spell can invalidate the trigger and probably should not be allowed pre-action.

As with many things in the books, standardization of wording would have made this clearer.

[sophontteks]

Case by case judgement is best.

Officially, the latest decision they've come to is that any bonus action that rides on the attack action requires the full attack action. This was the safest decision.

I'd keep that as a general rule, and make exceptions using your own judgement. One common exception is allowing the shield master bonus action first, as it was originally allowed to do so. But, the similiar polearm bonus action shouldn't because it requires all the attacks to use the polearm. The later allows some gamey shenanigans.

Beyond that one exception, specific scenarios may warrant an exception based on the rule of cool.