An on-hit item property is one that activates when the item it is on either hits something (for weapons) or is hit by something (for armor). In both cases, the "something" is the target of the on-hit property, while the item possessor is the "caster". There are three general groups of these properties — on monster hit, on-hit: cast spell, and general on-hit. The first of these only function when used on a creature weapon, while the second is the only type of on-hit property to be found on armor (in addition to being on weapons). The third group (general on-hit) is the focus of this article. Most of the time, multiple on-hit properties can co-exist on the same item; the sole exception is that only one (randomly determined) on-hit: cast spell property will fire for each hit (and each item, if applicable).
Many of the general on-hit properties are named for the effect they inflict upon their target. This is followed by (terse) information regarding how and when the effect is applied. As an example, an item property might be listed as "On Hit: Confusion DC-22 50% / 2 Rounds". This means that the item property will trigger for 50% of successful attacks. If it is triggered, the target is allowed a DC 22 saving throw. If the saving throw fails, the target will suffer confusion for 2 rounds. Exceptions to this naming scheme are those effects that either are instantaneous or last until cured (ability drain, disease, level drain, slay, vorpal, wounding). The type of saving throw is not listed in the item property, but it is usually one that is commonly associated with the effect in question.
* There is no saving throw for these item properties; instead the usual saving throw for the particular disease applies.
The level drain property drains a single level, and the wounding property wounds for a single hit point per round. The disease property has a DC listed that is not used. "Doom" is not a single effect, but is rather a combination of -2 penalties to attack rolls and skills (similar to the spell doom, but lacking the penalty to magical damage and saving throws). The poison variant does not use one of the poison effects, but instead applies d2 damage to the ability specified by the item property.
In addition to the effect on-hit properties, there are several general on-hit properties that trigger spells. For the most part, these can be replaced by the (newer) on-hit: cast spell properties, but standard items with these properties still exist (presumably because there was no reason to change them). For most of these properties (dispel magic, greater dispelling, lesser dispelling, and Mordenkainen's disjunction), the "DC" listed in the property is actually the caster level. The remaining spell (knock) is a bit of a special case. For on-hit: knock, the listed DC is the maximum unlock DC that can trigger this property. Specifically, this particular item property fires if the weapon damages a locked placeable or door whose unlock DC is less than or equal to the DC of the item property. If the item property fires, then the normal knock spell is cast (which can then unlock all nearby locked objects, regardless of their unlock DC).
See also: Category:On-hit