Anti-magic fields can be generated on most levels. They are also guaranteed on several special levels:
- the Knight quest locate level contains 7 anti-magic fields
- the Wizard quest locate level contains an anti-magic field
- almost every special level in Gehennom has at least one anti-magic field
Anti-magic fields drain between 2 and your experience level + 1 points of your spell power. If this would cause your spell power to go below zero, your maximum spell power will be permanently reduced by that amount, and your spell power becomes zero. Anti-magic fields have no effect on your maximum spell power if it is zero.
If you have magic resistance, you take damage instead of losing power. The damage is at least d4, with an additional d4 each if you:
- have half physical damage or half spell damage (non-cumulative)
- are wielding Magicbane
- are carrying an artifact which grants magic resistance by being carried; your own quest artifact is exempt.
The following information pertains to an upcoming version (3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.Per this commit, anti-magic fields now drain 2d6 energy and half that of maximum energy. If you have magic resistance, you take d4 damage in addition to the energy drain.
Effect on monsters
Monsters that have a special attack such as spellcasting or a breath weapon will also be affected by this trap. The timeout for their special attack increases by 2d2 turns unless they are magic resistant, in which case they lose HP. This will also reveal the trap. Other monsters do not trigger this trap and do not reveal it when they pass over it. 
When standing on an anti-magic field, you can dig down to replace it with a pit.
The following information pertains to an upcoming version (3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.Per this commit, anti-magic fields can be exploded by zapping cancellation at them.
These traps are usually harmless. In theory anti-magic fields could be harmful to some early-game spellcasters, especially pacifists who must cast healing often and cannot gain experience easily. Players who spend an early wish on a source of magic resistance may also be vulnerable.
Intentionally stepping on an anti-magic field is a somewhat risky way of identifying the cloak of magic resistance.
The anti-magic field was introduced in NetHack 1.3d.
- You feel your magical energy drain away.
- You are not magic resistant, and your Pw was drained.
- You feel momentarily lethargic.
- You are not magic resistant, but you have zero maximum Pw to drain.
- You feel sluggish.
- You are magic resistant, and took less than 1⁄4 your HP as damage.
- You feel very lethargic.
- You are magic resistant, and took more than 1⁄4 your HP as damage.
- You feel unbearably torpid!
- You are magic resistant, and were killed by HP loss.
- <monster> seems lethargic.
- A monster lost some Pw from an anti-magic field.
- <monster> is killed by the compression from an anti-magic field!
- A magic-resistant monster lost enough HP from an anti-magic field to die.