Spellcasting

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For monsters' spellcasting mechanics, see monster spells.

In NetHack, spellcasting is the act of casting a spell, done by using the Z command. Casting a spell uses your innate magical power as a source, rather than using an external source of magic such as a scroll or wand.

Healers, Monks, Priests and Wizards begin the game with knowledge of one or more spells, whose corresponding spellbooks appear in their initial inventory; other roles must find at least one spellbook and successfully read it first.

Basics

You must know at least one spell in order to cast; when casting a spell, a menu of known spells and their chance of failure is displayed. You can also view your list of known spells by pressing +, and pressing + again allows you to rearrange the spells so you can place them on more convenient letters.

A spell's chance of failure is affected by your spellcasting attribute (either intelligence or wisdom), experience level, skill level, your role's innate magical affinity, and what armor you are wearing: metallic armor in particular can impact chances of success, as well as any worn shield and their material if applicable. Failure rates can be reduced by wearing a robe, and can be additionally reduced further if the spell is an emergency spell or your role's special spell. For details, see the article section on how to calculate spell failure chance.

When you attempt to cast a spell, the game rolls for success or failure against this rate, with a message coming up if you failed to cast the spell; otherwise, the spell immediately takes effect, prompting for a direction if necessary. Training skills in spell schools is done by successfully casting spells in that school, and raises the percentage by an amount equal to the spell's level; the spell itself does not have to directly affect anything.

Casting spells requires a certain amount of energy and nutrition proportionate to the spell's level; failing to cast a spell correctly uses up only a portion of that energy, and the detect food spell does not drain nutrition when cast. Wizards have access to hungerless casting that can reduce or even eliminate nutrition costs, based on their intelligence score.

You cannot cast a spell if you lack the required energy, and in certain circumstances your energy or nutrition can be drained enough that an otherwise successful spell will end up failing; see spellcasting costs for further information. There are also other circumstances and requirements that can affect spellcasting:

• You cannot cast spells if you are stunned.
• Your strength must be at least 4 to cast a spell, unless you are trying to cast restore ability.
• You cannot be overtaxed or overloaded in terms of encumbrance.
• You must also be capable of physically vocalizing the spell to cast it – strangulation and polyforms that are headless, only make animal sounds or are otherwise incapable of speaking (e.g., grid bug, jabberwock, mimic, jaguar) will stop you from casting spells.
• You must also have at least one free hand to direct the energy – this means you cannot cast if there are cursed weapons or shields in both hands.
  • This only applies if you are in a form that has hands; polyforms that lack hands do not prevent you from casting.
• If confused, you can attempt to cast spells, but they will always fail with the same effects as random spell failure.

While using teleport at will is also considered to be a cast of a spell, and follows many of the same rules as casting teleport away, there are a few notable differences - teleport at will ignores failure rates, for instance.

Spellcasting costs

Each spell costs an amount of energy equal to 5 times the spell's level in order to cast; if you are carrying the Amulet of Yendor, it drains an amount of energy between 1 point and 2 times the usual cost as you attempt to cast.. If you do not have the required energy to cast the spell, nothing happens; if the Amulet drains enough energy to prevent the spell being cast, this uses up a move. If you have the energy for a spell and fail to cast it correctly, only half of that spell's energy cost (rounded down) is used up.

In addition, casting any spell other than detect food uses an amount of nutrition equal to two times the energy cost; this is usually 10 times the spell's level, before factoring in reduced-hunger casting for Wizards (hungerless casting ignores this entirely). A failed cast of a spell costs as much as a successful one, and carrying the Amulet has no impact on nutrition costs. Being weak and very close to fainting from hunger can prevent you from properly casting any spell other than detect food; fainting will outright prevent casting of those other spells, regardless of whether or not you have hungerless casting.

As an example, casting a level 3 spell normally requires 15 energy and 30 nutrition; if you fail to cast it, only 7 energy is used. When carrying the Amulet of Yendor, there is an energy penalty of 1 to 30 points, so the total energy cost varies from 16 to 45. The nutrition cost will always be 30 regardless of the circumstance.

Forgotten spells

Spell knowledge lasts for 20,000 turns after learning the spell from a spellbook; a spell is forgotten once this duration expires, and forgotten spells are marked with an asterisk * in the casting menu. Re-reading a spellbook for a spell with a timeout at or below 1,000 turns will refresh knowledge of that spell and reset the timeout to 20,000 turns; attempting to read a spellbook before the timeout is low enough will not use up a reading of the spellbook (meaning it will not result in a usage fee with unpaid spellbooks in a shop).

Attempting to cast a forgotten spell will leave you confused and/or stunned, with the duration dependent on the level of the forgotten spell; this does not consume any nutrition or power. The exact effects of casting a forgotten spell are as follows:

Probability	Effect
40%	confused for (spell-level + 1) * 3 turns
30%	confused for (spell-level + 1) * 2 turns stunned for (spell-level + 1) turns
20%	confused for (spell-level + 1) turns stunned for (spell-level + 1) * 2 turns
10%	stunned for (spell-level + 1) * 3 turns

Forgotten spells are a common way to deliberately become confused and invoke the alternative effects of certain scrolls.

Calculating spell success rate

The spell failure rate given in the spellcasting menu is calculated using the listed algorithm below, and the values in the table below this list, with higher numbers signifying harsher penalties (limited to a maximum of 20):

• Start with the "base" value associated with your role.
• Each role also has an "Emergency" modifier for emergency spells - specifically, remove curse and all healing spells except for stone to flesh - that is applied when casting such a spell.
• If you are wearing any shield, add the amount in the "shield" field. Though these amounts are small, note that wearing any shield other than a small shield also incurs a severe penalty later in the success chance calculation.
• If you are wearing metallic body armor, add the amount in the "Suit" field.
  • If you are also wearing a robe, only add half the amount (rounded down).
  • If you are wearing a robe without metallic armor, then subtract the amount in the "Suit" field.
• If you are wearing a metallic helmet other than the helm of brilliance, add 4.
• If you are wearing metallic gloves, add 6.
• If you are wearing metallic boots, then add 2.
• If you are casting the corresponding special spell for your role (also listed in the table), subtract 4.

Class	Base	Emergency	Shield	Suit	Stat	Special spell
Archeologist	5	0	2	10	Int	Magic mapping
Barbarian	14	0	0	8	Int	Haste self
Caveman	12	0	1	8	Int	Dig
Healer	3	-3	2	10	Wis	Cure sickness
Knight	8	-2	0	9	Wis	Turn undead
Monk	8	-2	2	20	Wis	Restore ability
Priest	3	-2	2	10	Wis	Remove curse
Ranger	9	2	1	10	Int	Invisibility
Rogue	8	0	1	9	Int	Detect treasure
Samurai	10	0	0	8	Int	Clairvoyance
Tourist	5	1	2	10	Int	Charm monster
Valkyrie	10	-2	0	9	Wis	Cone of cold
Wizard	1	0	3	10	Int	Magic missile

The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that the information below is still accurate, then update the page to incorporate it.

Knights can now cast clerical spells as if they were not wearing metallic body armor, including the bonus for any worn robes.

Next, calculate your base chance of success, which is 5.5 times either your intelligence or wisdom depending on your role (see the "Stat" field). The maximum natural human Int/Wis of 18 gives a 99% base success rate. This chance is modified by the following factors:

• SKILL level (Unskilled = 0, Basic = 1, Skilled = 2, Expert = 3)
• spell level (LVL)
• experience level (XL)

The formula used to modify this chance is:

difficulty = (LVL * 4) - (SKILL * 6) - (XL/3) - 5

If difficulty is positive, the spell is considered difficult. Your chance is reduced according to the following formula. A difficulty of 1 therefore gives a 53% penalty, and a difficulty of 9 gives a 100% penalty.

$\text{chance} = \text{base chance} - \sqrt{(900 \times \text{difficulty}) + 2000}$

If it is negative, it will be increased with diminishing returns: the absolute value is multiplied by (15/LVL), capped at 20, and added to the base chance. A level 1 spell therefore achieves the full 20% bonus with a difficulty of -2. A level 7 spell cannot achieve a better difficulty than -5, which gives a bonus of 10%.

The resulting chance is clipped to the range of 0% to 120% success. If you are wearing a shield larger than a small shield, the chance is then reduced to ¹⁄₄ of the amount, or else halved if it is the special spell for your role Finally, the chance of success is adjusted by your total penalty using the following formula:

$\text{actual chance} = \frac{\text{chance} \times (20-\text{penalty})}{15} - \text{penalty}$

The result is clipped to the range of 0% to 100% success.

One non-obvious consequence of this calculation is that sometimes gaining an experience level divisible by 3 can have a very large effect on the success rate of some spells.

Spell Level	Skill Level	XL for large improvement
2	unskilled	9
3	unskilled	21
4	basic	15
5	basic	27
5	skilled	9
6	skilled	21
7	expert	15

Minimum spell failure rates

Because "chance" in the above section is capped at 120%, there is a point where improving your skill, spellcasting stat, or level will not decrease spellcasting failure rates. The only way to decrease failure rates below the listed minimum is to reduce your spellcasting penalty (by putting on a robe or removing penalizing armor). The following table shows the minimum spell failure rates for a given penalty, not including the penalty change of -4 from your special spell:

Penalty	Min. failure rate	...with large shield	...with large shield, special spell
≤-4	0	60+3*penalty	0
-3	0	51	5
-2	0	54	10
-1	0	57	15
0	0	60	20
1	0	63	25
2	0	66	30
3	0	69	35
4	0	72	40
5	0	75	45
6	0	78	50
7	3	81	55
8	12	84	60
9	21	87	65
10	30	90	70
11	39	93	75
12	48	96	80
13	57	99	85
14	66	100	90
15	75	100	95
16	84	100	100
17	93	100	100
≥18	100	100	100

Effects

Many spells have a corresponding wand, scroll or potion whose effects are similar or exactly the same.

Range

The distance of a beam-type spell ranges from 6–13 squares. The distance of the ray from a spell of dig ranges from 8–25 squares; all other ray-type spells have a range of 7–13 squares.

To-hit

For applicable offensive spells, the chance of hitting a target with a given AC is based on a d20 roll, with an additional to-hit bonus calculated by taking the sum of penalties and bonuses from both your dexterity and the relevant spell skill (-4 for unskilled, +2 for skilled, or +3 for expert). Unlike physical combat, no other bonuses apply.

If the d20 roll is exactly 1, it's changed to a random number between -6 and 3. Otherwise, if AC is negative, its value is instead weakened to a random number between -1 and itself. Either way, the to-hit bonus and AC value are added to the roll, and if the sum is greater than 4, the spell hits.

Damage

A spell damage bonus based on intelligence (INT) and experience level (XL) is used in most attack spell damage calculations:

Criteria	Bonus
INT <= 9	-3
INT <= 13 OR XL < 5	0
INT <= 18	+1
INT <= 24 OR XL < 14	+2
INT = 25	+3

Each spell has its own damage calculations that usually include this bonus in some manner:

• Force bolt:
  • 2d12 + spell damage bonus
• Drain life:
  • base d8
    • d4 for level 0 monsters
    • 4-8 for adult dragons
    • 5-8 for named demons (though they are normally immune)
    • (base health) / (base level) for golems
  • Spell damage bonus is added after factoring the above, then damage is halved if the monster resists: otherwise, the spell deals double damage and also inflicts damage to max HP
• Magic missile:
  • (XL / 2 + 1)d6 + spell damage bonus
  • no damage if the monster has magic resistance
• Cone of cold (below Skilled):
  • (XL / 2 + 1)d6 + spell damage bonus; additional (XL / 2 + 1)d3 if monster has fire resistance
• Fireball (below skilled)
  • Base 12d6 damage explosion centered at the monster; no spell damage bonus
  • modified like Skilled below
• Cone of cold and fireball (skilled or expert)
  • 2 to 9 explosions covering a 3 x 3 space, the first centered on a starting point up to 10 steps away, remaining ones randomly shifted up to one tile from there
  • XL / 2 + 1 + spell damage bonus on each monster in affected space for each explosion
  • Cone of Cold and monster has fire resistance or Fireball and monster has cold resistance: double damage
  • Monster resists: 1/2 damage
  • additional damage for destroyed items

Strategy

The three primary methods to improve your spellcasting rates are:

• Increasing the relevant spellcasting attribute.
• Increase your skill in the desired spell school(s).
• Wear armor appropriate to your role's spellcasting abilities.

Role and attribute strategy

Your casting attribute, role Base value (per the above table), and metallic armor determine your success chance for low-level spells. Experience level and spell school skill can raise your chance for high-level spells up to the chance of low-level spells, but will not make low-level spells more reliable.

Each point of your spellcasting attribute up to 16 is significant in determining your success chance with "easy" spells. Roles with lower base spellcasting penalties (i.e. "base" values of 5 or lower) may be able to get by with fewer points in that attribute, but tend to start with that attribute at the racial maximum in any case. An intelligence or wisdom score of 17-18 is significant for roles with higher base penalties or low-penalty roles wearing metallic armor; score of 19-22 are significant for high-level spells that the 20-point "easy" bonus does not apply to; and scores of 23 or higher are only significant for "difficult" spells, which generally have low success chances regardless.

With a base success chance of 120%, your spellcasting penalty (Base modified by armor) must be 6 or less to achieve an overall 100% success chance. Roles that can achieve this without a robe are Archeologist, Healer, Priest, Tourist, and Wizard. Roles that can achieve this when casting emergency spells or their special spell are Knight and Monk. Roles that can achieve this with their special spell only are Ranger, Samurai, Rogue, and Valkyrie. The remaining two roles, Barbarian and Caveman, cannot achieve 100% success chance in any spell without a robe.

Skill and experience strategy

Spells are much easier to cast when their difficulty is zero or less. The following table lists the most difficult spell level that is still considered easy (i.e. with no penalty for spell level) given a set of particular experience and skill levels.

Highest easy spell level
Xlvl	Unskilled	Basic	Skilled	Expert
1–2	1	2	4	5
3–8	1	3	4	6
9–14	2	3	5	6
15–20	2	4	5	7
21–26	3	4	6	7
27–30	3	5	6	7

If your Intelligence or Wisdom is high, spells of this level or below are likely to have a near-100% base success chance. It is still possible to cast non-easy spells, but they tend to have much lower success chances. One exception is a high-level Monk wearing a robe; they get enough of a bonus from it that even difficult spells of up to level 5 can be 100% reliable. With 22 wisdom from a helm of brilliance, level 6 spells can also have a 100% success chance.

Armor strategy

Some heroes wear metal armor most of the time and take it off specifically for noncombat/postcombat spellcasting (e.g., clerical, divination and healing spells), or when preparing for combat (e.g., protection, confuse monster, and haste self). Others are primarily offensive spellcasters, and may eschew metal armor or wear robes so that they may freely use attack and enchantment spells as they encounter monsters. In general, armor selection is always tailored to a character's spellcasting approach.

In the early game, even Wizards will sometimes wear metal armor; any hero who has depleted their energy may as well wear metal armor while they regain energy. In the late game, most of the ascension kit armor items, e.g. speed boots, helms of brilliance and dragon scale mail, do not hinder spellcasting anyway. Depending on the role, high-level and high-intelligence characters often have good spellcasting success rates, even if they wear gauntlets of power and/or a small shield.

Messages

The magical energy is released!

You cast a directional spell, but did not answer a valid direction.

History

Spellcasting is introduced along with spellbooks in NetHack 1.3d. A spell first had to be learned by transcribing it from the spellbook, which would then disappear from your inventory afterward - if the transcription was successful, you could then use the #cast extended command to use the spell. Transcribing a spell would always fail and use up the spellbook if you were blind or confused. A given spell had a limited number of castings before it expired, and another spellbook is required in order to re-learn the spell. Armor interactions with spellcasting were introduced in NetHack 3.2.0, and the integration of the Wizard Patch into NetHack 3.3.0 marks the origin of the current spellcasting system.

In NetHack 3.6.0 and previous versions, including some variants based on these versions, the Amulet of Yendor would increase the cost of casting a spell, instead of draining energy as you tried to cast it. This meant that it would also increase the nutrition cost, and it would not prevent emergency uses of a spell. In the example above of casting a level 3 spell, if you had only 16 energy left, you could still try again and again, without using any time, until the random penalty is rolled as 1. This was fixed in NetHack 3.6.1.

Variants

Many variants of NetHack end up making changes to the spellcasting system in some manner.

SLASH'EM

SLASH'EM makes several changes to NetHack's spellcasting: New spells have been added, and several existing ones have been reshuffled. SLASH'EM roles also tend to be more proficient in spell skills than their vanilla counterparts.

FIQHack

FIQHack has many changes to spellcasting for both players and monsters:

• There are four new spells, all of which are level 7:
  • Charging (enchantment), which is equivalent to an uncursed scroll of charging.
  • Phase (escape), which gives 21-60 (additional) turns of phasing.
  • Astral eyesight (divination), gives 11-30 turns of astral vision.
  • Summon nasty (clerical), which is equivalent to the vanilla monster spell and summons tame monsters if you target a hostile monster.
• The spell of identify is altered:
  • When cast at unskilled, the spell only identifies object type, appearance, and artifacts.
  • At Basic, it also IDs enchantment, object properties, charge count, tin content and egg type.
  • At Expert, the spell identifies fooproof state.
• Various other spells have their levels changed:
  • Dig is level 2
  • Identify is level 2
  • Cancellation is level 5
  • Teleport away is level 5
  • Polymorph is level 7
  • Create familiar is level 2
• The spell of create monster is replaced with the spell of summoning. Summoned monsters disappear after a set number of turns, based on casting skill.
• Magic missile does less damage if cast at levels lower than expert.
• Spellcasting no longer exercises wisdom; some spells can be maintained, which slowly drains energy but provides a continuous effect.
• Instead of a spell failure percentage, the amount of power required to cast a spell changes:
  • Spell cost is (base cost) * 100 / success%. Force bolt costs 5pw at 0% fail, 10pw at 50% fail, 20pw at 75% fail, 500pw at 99% fail, 1000pw at 100% fail (treated as 99.5%)
  • The Amulet doubles spell cost, instead of randomly draining 2-3x energy per spell.
• Monsters use the same spellcasting system as players, which means that high-level spellcasting monsters have a lot of energy and can cast multiple spells quickly. Monsters can also pick up and read spellbooks to gain new spells.
  • The curse items monster spell no longer exists, but certain curse effects are stronger and more common.
  • Bones ghosts may be replaced by equivalent player monsters with the same spells as the late player.

External links

• NetHack Spell Failure Rate Calculator (JavaScript)
  • Older version of the above

References

This page is based on a spoiler by Dylan O'Donnell. The original license is:

Redistribution, copying, and editing of these spoilers, with or without modification, are permitted provided that the following conditions are met:

1. The original contributors to any spoiler must continue to be credited.
2. Any modifications to the spoiler must be acknowledged and credited.