The defense is obligated to offer alibi witnesses and their phone numbers and addresses, expert witnesses, and any witnesses it wishes to present in support of an affirmative defense, which includes defenses like diminished capacity, coercion, insanity, alibi, self-defense, etc.

The defense does not have to provide the names of any rebuttal or fact witnesses. Sometimes the court will ask how many witnesses they plan to present in order to calendar the trial appropriately. Usually, the prosecutor can figure out who the witnesses are likely to be, and they can always request an offer of proof where they are not sure what the witness is going to say.