Sage Advice : Adventuring
Is there a hard limit on how many short rests characters can take in a day, or is this purely up to the DM to decide?
The only hard limit on the number of short rests you can take is the number of hours in a day. In practice, you’re also limited by time pressures in the story and foes interrupting.
Are extradimensional spaces, such as a demiplane or the space created by rope trick, considered to be on a different plane of existence?
An extradimensional space (aka an extraplanar space) is outside other planes. Therefore, if you’re on the Material Plane and your foe is in an extradimensional space, the two of you aren’t on the same plane of existence.
How do I tell if something in the game is magical?
For an extensive discussion of this topic, see the question "Is the breath weapon of a dragon magical?"
What’s an example of an effect that can reduce exhaustion?
The greater restoration spell can reduce exhaustion.
Is there a way to get lost Intelligence back, such as after an intellect devourer zeroes it?
The greater restoration spell can remove the reduction to an ability score.
What happens after 20th level? Is there a cap to character levels?
The highest level is 20th. The "Epic Boons" section in the Dungeon Master’s Guide (p. 231) offers ideas for further advancement.
Written by Jeremy Crawford (Sage Advice Compendium v2.3)