How obvious is Mage Armor?

Question

Can an observer see that a creature is under the effect of the Mage Armor spell?

Answer 1

Undefined

The closest we get to a description is:

You touch a willing creature who isn’t wearing armor, and a protective magical force surrounds it until the spell ends.

which tells us nothing about the appearance of this protective magical force.

Ask your DM for a ruling. Feel free to argue that it would be cooler if it were/were not visible, or that it would make more sense if it were/were not visible, or that the caster should be able to decide when casting, or whatever. There is no universal ruling.

Answer 2

Spells only do what they say — the spell's effect doesn't indicate that it creates any visuals, so it has none.

DMs can rule that this spell works otherwise in their own settings, but as-written it's invisible.

Answer 3

Magical force is usually visible; mage armor remains ambiguous

Other spells/effects than mage armor deal with magical force:

• Armor of Agathys involves a protective magical force, but looking at the spell it is probably related to the cold counter-damage.
• Given that imprisonment's other effects all have visible manifestations, we could reasonably conclude that the sphere of magical force created by its "Burial" effect is also visible.
• Leomund's tiny hut "is opaque from the outside... but it is transparent from the inside."
• Otiluke's resilient sphere shimmers.
• Mage armor and Tenser's floating disk doesn't say what it looks like. (A disk might be a shape that would have to be visible to be discerned, or it might be simple enough that it need not be visible to be reasonably described as a disk.)
• Forcecage, shield, unseen servant, and wall of force are all invisible.

Additionally, PHB defines force damage type as "pure magical energy focused into a damaging form." The following spells/effects, then, also are related to/composed of magical energy:

• Banishing smite states that the imbued weapon "crackles with force" as it deals its extra force damage. This sounds like a subtle but noticeable effect (moreso to observers than the smitten).
• Bigby's hand is composed of "shimmering, translucent force," which is capable of dealing force damage as a possible effect.
• Disintegrate manifests as "a thin, green ray."
• Eldritch blast is "a beam of crackling energy."
• Magic missile creates "glowing darts."
• Given that Mordenkainen's sword is "sword-shaped," it is probably visible. (How could anyone tell it were sword-shaped otherwise?)
• Spiritual weapon is spectral.
• Most DMG magic items follow this trend of force damage being visibly inflicted.
• Beholders and beholder zombies deal force damage with their disintegration rays.
• Ghosts and other spectral beings are dealt force damage if they end their turn in a solid object, a visible effect.
• Poltergeists are invisible; it stands to reason their "Forceful Slam" is as well.
• Dimension door, etherealness, and teleport don't say what it looks like if they cause force damage.

Given that most effects dealing with magical force are visible, I would rule (and acknowledge that it is a ruling more than an answer) that mage armor is visible, probably as a shimmer or glow.

Answer 4

nothing wrong with adding flavor to it. For example you could make you armor appear to encase your character like a guyver suit, witchblade armor or a Venom Symbiote activation. Another person might make it look like shimmering translucent armor almost like a celestial prortection. And still another might make it appear as a dome of protection barely visible unless it is "struck". Describing your spells is part of the fun I believe. After all since the Dr. Strange movie I see a lot of the Round arcane writing type of thing for shield spell now, that is obviously a very flavorful description of the spell.