Does using a shield add to your AC bonus and/or end the spell early?

So the main difference is just not being able to dismiss the spell at will as an action? Oh and it's available for wizards twice

You have to have Shield Armour Training to gain the benefits from a shield and it does fall under the armour section in the 2024 PHB so I would sadly say that it will end this spell early yes. 

Page 219

“anyone can don armor or hold a shield” (need training)

On same page “wear one suit of armor or wield only One shield at a time”

seems to still work with mage armor (shield) if proficient 

Quote from Menwy >>

Page 219

“anyone can don armor or hold a shield” (need training)

On same page “wear one suit of armor or wield only One shield at a time”

seems to still work with mage armor (shield) if proficient 

 The spell also says that 'The spell ends early if the target dons armor.' and to me the rules are saying that a shield is armor so it would end if you were to don the shield. 

I am not a fan of it and I may allow a shield and mage armor at my table but if you are doing 2024 RAW then no.

Quote from Matt77stock >>

So the main difference is just not being able to dismiss the spell at will as an action? Oh and it's available for wizards twice

The general spellcasting rules in the 2024 PHB say that any ongoing spell can be ended by the caster without using an action, so all the spells that had specific provisions for that have had those removed.

Quote from hjl247 >>

Does using a shield add to your AC bonus and/or end the spell early?

Using a shield doesn't negate Mage Armor. This was clarified in the Sage Advice Compendium and there's nothing in the 2024 PHB that contradicts it.

However, keep in mind that you do not get the AC benefit from a shield if you do not have training with shields. So, if you don't have shield training, you can pick up a shield without ending this spell's effect on you, but doing so won't provide any benefit. And Sorcerers and Wizards (the classes that generally have access to this spell) do not get shield training from their class. You can get it from the Lightly Armored feat or by multiclassing into some other classes.

You can “don” armor (wear it) or “hold” a shield. You can’t really don a shield. That would be a fashion faux pas.

Last line of the Shield of the Cavalier and other shields.

Shields require the Utilize action to Don or Doff. You gain the Armor Class benefit of a Shield only if you have training with it.

My main question is does this stack with Unarmored Defense features from various classes?

If so, I could see a Barbarian/College of Dance Bard/Monk/Draconic Sorcerer getting a lot of value out of this since the spell's range is touch.

I could see the spell disabling these features since Mage Armor is technically armor, but at the same time, it doesn't fall into a light/medium/heavy category either, which would mean Unarmored Defense bonuses would still apply.

Armor Class in the Rules Glossary: "If a rule gives you another base AC calculation, you choose which calculation to use; you can’t use more than one."

Quote from GamingPaladin >>

My main question is does this stack with Unarmored Defense features from various classes?

If so, I could see a Barbarian/College of Dance Bard/Monk/Draconic Sorcerer getting a lot of value out of this since the spell's range is touch.

I could see the spell disabling these features since Mage Armor is technically armor, but at the same time, it doesn't fall into a light/medium/heavy category either, which would mean Unarmored Defense bonuses would still apply.

It does not stack with any other way of determining your base Armor Class, no. If you have more than one way of determining your base Armor Class, you choose which one you want to use (generally, the one that leads to a higher AC).

However, it is also worth pointing out that there is nothing anywhere saying that this spell is "technically armor"; it isn't armor, and it would not invalidate some other effect that only worked while not wearing armor.

Is the Mage Armor visible?

Quote from Druidduo >>

Is the Mage Armor visible?

The spell doesn't say it is, so I would say no, unless you want to flavor it that way.

Can you cast it on yourself?

If another class gives cha or wizdom to ac does it stack with Mage armor?

yes if you are willing, you can touch yourself.

Quote from HollowB55 >>

If another class gives cha or wizdom to ac does it stack with Mage armor?

It depends on how it's worded. Mage Armor changes your base AC calculation, so it doesn't stack with other effects that also change your base AC calculation. This includes things like the Unarmored Defense feature from the Barbarian and Monk classes, as well as the Draconic Resilience feature from the Draconic Sorcery subclass. You can only have one base AC at a time.

However, if you had a class feature that said something like "you gain a bonus to your Armor Class equal to your Wisdom modifier", then that would stack with Mage Armor, because that's providing a bonus to AC rather than changing your base AC. As far as I know, there aren't any existing official features that do this, though.

Quote from Grey_sun_the_second_the_first >>

Can you cast it on yourself?

All spells with a range of Touch can be applied to the caster themselves unless the spell specifically says something like "a creature other than you".