So I’m playing a 1st level bard with 4 levels in warlock (The rest of the players think I’m just a bard) and I was wondering if I can cast warlock spells using bard slots are vice versa. As level a level 1 bard I have 4 1st level spell slots and I have 2 2nd level slots from the warlock. Do the rules determine if I can cast warlock spells at first level with bard slots or is that up to DM discretion?
I believe that the rules on multiclassing have the answers to your questions.
Check the paragraph on Spellcasting, and more specifically the "spell slots" part (and don't skip over the "Pact Magic" bit, since one of your classes is a Warlock).
Yes. You can use spell slots interchangeably for casting warlock and bard spells.
However, spell slots and pact magic slots don't combine when multiclassing. As a result, a level 1 bard has 2 first level slots and a level 4 warlock has 2 second level slots so you have a total of 2 first and 2 second level slots. Your post mentioned 4 first level spell slots and 2 2nd level slots which is not correct.
So I’m playing a 1st level bard with 4 levels in warlock (The rest of the players think I’m just a bard) and I was wondering if I can cast warlock spells using bard slots are vice versa. As level a level 1 bard I have 4 1st level spell slots and I have 2 2nd level slots from the warlock. Do the rules determine if I can cast warlock spells at first level with bard slots or is that up to DM discretion?
I believe that the rules on multiclassing have the answers to your questions.
Check the paragraph on Spellcasting, and more specifically the "spell slots" part (and don't skip over the "Pact Magic" bit, since one of your classes is a Warlock).
The short answer is yes, you can cast either spell type using either spell slot type.
Short answer: yes
Long answer: read the multiclassing rules.
[Edit]Ah, someone beat me to it.
Thanks guys. I don’t actually own a copy of the PHB so that helps.
https://www.dndbeyond.com/compendium/rules/basic-rules/customization-options#Spellcasting
Yes. You can use spell slots interchangeably for casting warlock and bard spells.
However, spell slots and pact magic slots don't combine when multiclassing. As a result, a level 1 bard has 2 first level slots and a level 4 warlock has 2 second level slots so you have a total of 2 first and 2 second level slots. Your post mentioned 4 first level spell slots and 2 2nd level slots which is not correct.
If you use the Dndbeyond builder it shows that its allowed. When you cast a spell it gives you an option; cast: [warlock] [bard].
It shows this for ALL spells you have regardless of source which makes it safe to assume that you can