Arcane spell failure

Arcane Spell Failure is the chance that an arcane spell — that is, one from the Bard, or Sorcerer/Wizard spell list — will fail to be cast due to interference from the caster's armor or shield. Such a failure expends the spell's spell points and cooldown as if it had been cast. Bard spells are not supposed to be subject to Arcane Spell Failure when wearing light armor but scrolls shared by Bards and Sorcerers/Wizards are bugged and still roll for an ASF check; same with Artificers and divine casters and scrolls shared with Sorcerers/Wizards (see below).

The ASF chances from your armor and your shield add together.

Casting a spell from a wand is not subject to ASF, but reading a scroll is.

Spells that don't need a somatic component are not subject to ASF, either when cast or read from scrolls.

Bugged Scrolls
Any scroll with a spell on the Sorcerer/Wizard's list will be susceptible to "Arcane" Spell Failure even if the reader is an Artificer, Bard wearing light armor, or divine caster. (Thus, Clerics cannot reliably use Protection from Energy scrolls in their heavy armor). This behavior may be modified in the future, as developers have acknowledged it should not work this way.

Similar to divine spells, Artificer-exclusive spells are Arcane-type spells but are not subject to Arcane Spell Failure. Artificers using Sorcerer/Wizard's list scrolls via UMD are subject to Arcane Spell Failure. So, anyone using a Lightning Motes scroll suffer no Arcane Spell Failure, but an Artificer is susceptible to Arcane Spell Failure when using a scroll of Fire Shield (not Artificer at all) or Reconstruct (available to Artificer but not Artificer-exclusive).

Due to this same bug, Bards wearing light armor using scrolls on the Sorcerer/Wizard's list will be susceptible to Arcane Spell Failure, even if the spell exists on the Bard spell list as well. So, a Bard wearing light armor has no chance of ASF when casting Greater Heroism as a spell, but is susceptible to Arcane Spell Failure when casting it from a scroll.

Reducing Failure Chances
Both Mithral & Twilight armor and shields reduce the Arcane Spell Failure chance by 10%. These effects stack and in some cases completely negate the Arcane Spell Failure of a given item. Darkleaf armors have a slightly lower Arcane Spell Failure chances (5% less), but this material is used for rather heavy armors (Breastplate and Bandedmail.) and cannot completely negate ASF alone.

Arcane Spell Failure is of particular importance to Warforged arcane casters since their natural body plating imposes at least a 5% ASF penalty by default. Fortunately, there are ways to mitigate it. Composite and Mithral body plating are considered light armors and thus don't impact Bards. At level 2, a Warforged character can get the Warforged Inscribed Armor I enhancement to reduce ASF from armors by 5%, thus removing ASF when having Composite Plating. At level 6 they can select Warforged Inscribed Armor II to reduce it by a total of 10% and at level 10 can get Warforged Inscribed Armor III to reduce it by a total of 15%.

Elves may also reduce Arcane Spell Failure with their Elven Arcane Fluidity line of Enhancements. At level 2, they may reduce ASF by 5% on Light armor. At level 6, by 5% on Light or Medium armor (this is not cumulative). Finally, at level 14, they can get Elven Arcane Fluidity IV: for a 20% ASF reduction on light armor 15% ASF reduction on medium armor and a 10% ASF reduction on heavy armor or shields. It means the best reduction an Elf can have is 20%.

Warchanter II receives 0% spell failure in medium armor as an extension of the Bardic abilities in light armor and bypasses the check entirely where other types of Bards still receive a check in some circumstances.


 * Lesser Arcane Casting Dexterity is -5% ASF (available as a Prefix on Ring, Trinket, or Gloves via Cannith Crafting)
 * Arcane Casting Dexterity is -10% ASF (available on the Seven Fingered Gloves)
 * Lesser Arcane Sigil is -5% ASF (available as a Prefix on Docents via random loot generation or Cannith Crafting)
 * Arcane Sigil is -10% ASF (available as a Prefix on Docents via random loot generation or Cannith Crafting)

The Blue Augment Crystal of Agile Casting in an Epic Blue Augment Slot also give -15% ASF which will not stack with Arcane Casting Dexterity but will stack with Arcane Sigil.