# Spellbook of protection

spellbook of  +   protection   

Appearance

random

Abundance

1.83%

Base price

100 zm

Weight

50

Turns to read

3

Ink to write

5–9

Spell type

clerical

Level

1

Power cost

5 Pw

Direction

non-directional

In NetHack, the spellbook of protection allows the player to learn the protection spell. The spell is unrelated to protection granted by priests or praying.

Contents

1 Generation
2 Effects

2.1 AC granted

3 Messages
4 Strategy
5 Variants

5.1 dNetHack
5.2 FIQHack

6 References

Generation
Monks have a 1/3 chance of starting with a spellbook of protection.[1]

Effects
Casting this spell decreases your AC temporarily; the exact reduction depends on your experience level, the amount of protection already gained from this spell, and your AC before casting the spell. The protection wears off at a rate of 1 point every 10 turns, or 1 point every 20 turns if the spell was cast with expert proficiency.

AC granted
The exact formula for determining the granted protection[2] is whichever of the following two is more:

or

where "prior spell AC" is the AC already gained from castings of the protection spell; "other AC" is 10 minus your AC but for the spell, including all armor bonuses and divine protection; and log2(XL) is just the logarithm with base 2, according to the following table:

Experience level
log2(XL)

1
0

2-3
1

4-7
2

8-15
3

16-30
4

Thus you will get 1-5 AC on the first casting depending solely on level, and on subsequent castings you will get progressively less depending on your AC and protection level.

XL

Other AC

Total AC from n castings

1
2
3
4
5
6
7
8
9

1
10 to 1
1
2
3
4
4
4
4
4
4

1
0 to -9
1
2
3
3
3
3
3
3
3

1
-10 to -19
1
2
2
2
2
2
2
2
2

1
&lt;-19
1
1
1
1
1
1
1
1
1

2-3
10 to 1
2
4
5
6
7
8
8
8
8

2-3
0 to -9
2
4
5
6
6
6
6
6
6

2-3
-10 to -19
2
3
4
4
4
4
4
4
4

2-3
&lt;-19
2
2
2
2
2
2
2
2
2

4-7
10 to 1
3
6
8
9
10
11
12
12
12

4-7
0 to -9
3
5
7
8
9
9
9
9
9

4-7
-10 to -19
3
5
6
6
6
6
6
6
6

4-7
&lt;-19
3
3
3
3
3
3
3
3
3

8-15
10 to 1
4
7
10
12
13
14
15
16
16

8-15
0 to -9
4
7
9
10
11
12
12
12
12

8-15
-10 to -19
4
6
7
8
8
8
8
8
8

8-15
&lt;-19
4
4
4
4
4
4
4
4
4

16-30
10 to 1
5
9
12
14
16
17
18
19
20

16-30
0 to -9
5
9
11
13
14
15
15
15
15

16-30
-10 to -19
5
8
9
10
10
10
10
10
10

16-30
&lt;-19
5
5
5
5
5
5
5
5
5

Messages
The 

<air> around you begins to shimmer with a golden haze.
You cast the protection spell.
The golden haze around you becomes more dense.
You cast the spell while already protected by it.
Your skin feels warm for a moment.
You cast the spell while already at the maximum amount of protection.
The golden haze around you becomes less dense.
The spell is wearing off.
The golden haze around you disappears.
The spell has worn off completely.
Strategy
The spell is an easy means of training skill in clerical spells. If you see a difficult or out-of-depth monster nearby and are willing to fight it, casting protection before engaging it is often a good idea. The spell is also useful if you are taking many hits from several monsters and/or already battling a difficult or out-of-depth monster.
Monks who start with this spell may find it useful to make up for their lack of armor in the early game, and should cast it before any prolonged fight.

Variants
dNetHack
The protection spell functions differently in dNetHack. Multiple castings of protection do not stack. When you cast the spell, it grants an AC bonus based on your experience level.

Experience level

AC bonus

1

2

2 to 3

4

4 to 7

6

8 to 15

8

16 to 30

10

Casting the spell again resets your bonus to this level and refreshes the wear-off countdown. This protection wears off over time based on your casting skill at the time you cast the spell.

Casting skill

1 point wears off after

Expert

30 turns

Skilled

20 turns

Basic

15 turns

Unskilled

10 turns

If your unprotected AC is greater than 0 then it is set to 0 before this bonus is applied.  

FIQHack
In FIQHack the protection spell only works if you are not wearing body armor.

References

↑ u_init.c in NetHack 3.4.3, line 654

↑ cast_protection in Spell.c

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