The Spell Nondetection Says:
The target can't be targeted by any divination magic or perceived through magical scrying sensors.
My impression is that the intent of Nondetection is to keep something hidden. However there are some Divination school attack spells likeMind Spike.
Will Nondetection prevent Mind Spike (and other divination attack spells) from targeting a creature, even if it is visible and right in front of you?
The mind spike spell it a Divination spell and it has a target. Meanwhile, nondetection prevents you from being targeted by any Divination magic. If the rules wanted this to only apply to a certain subset of Divination spells, the rules would include text indicating that that is the case. Lacking such text, we know it applies to any and all Divination spells, completely indiscriminately.
Thus, nondetection means you cannot be targeted by mind spike, a Divination spell.
It's not quite clear to me from the question alone how all divination spells would be affected. Let's journey to the answer.
As Medix's answer indicates, clearly Mind Spike is a no. The target is you and Nondetection prevents you from being targeted. Done and done.
But area effects are less clear. If you are a fiend, does Detect Evil and Good target you? It does not, the target is Self with a range of 30 feet. To me this feels like the difference in direct attacks and AOE's for things like the Ioun Stone of Absorption
While this pale lavender ellipsoid orbits your head, you can use your reaction to cancel a spell of 4th level or lower cast by a creature you can see and targeting only you.
But the description is very specific. The Staff of the Magi is similarly specific about which spells it can absorb. Our Nondetection description is more vague.
So let's look at the full text of the spell:
For the duration, you hide a target that you touch from divination magic. The target can be a willing creature or a place or an object no larger than 10 feet in any dimension. The target can't be targeted by any divination magic or perceived through magical scrying sensors. [Emphasis mine]
Now it's doing more than the quoted text in the question. We are hiding the target from divination magic, not just keeping it from being targeted by divination spells. Now it's easier to say that the target is hidden from our divination Detect Evil and Good spell that isn't specifically targeting it. It's also clear the target will be safe from detection from:
There are some that might need DM decisions, but really all of these seem like they would fail:
Anyway, I just want to add, since I'm looking at spells, that there are some spells that aren't going to work while the caster/friendly target is under Nondetection, so beware:
One last area: Diviners. Subclass eatures aren't spells, they're definitely magical, and Nondetection works against Divination Magic, not just divination spells. Thus I would rule that a Diviner couldn't use a portent against a "Nondetected" creature, nor could the Diviner use one on themselves if they were Nondetected. Third eye is right out as well.
