Bag of holding

(
Name	bag of holding
Appearance	bag
Base price	100 zm
Weight	15
Material	cloth
Monster use	Will not be used by monsters.

A bag of holding is a magical tool that appears in NetHack. Placing items into a noncursed bag of holding reduces their weight, making it one of the most coveted objects for general use.

Generation

The prize at the end of Sokoban always has a 50% chance of being a bag of holding, and will otherwise be an amulet of reflection.

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.

Both prizes are no longer equally likely for each floor. Instead, floor 4a has a 75% chance for a bag of holding, and 4b has a 75% chance for an amulet of reflection.

Weight change

The weight of a bag of holding, including the 15 aum for the bag itself, depends on the weight of its contents ($cwgt$) and its BUC:

BUC	total weight
blessed	$15 + (\frac{cwgt}{4} + 1)$
uncursed	$15 + (\frac{cwgt}{2} + 1)$
cursed	$15 + (cwgt \times 2)$

Generally speaking: bags of holding halve the weight of its contents, blessed bags divide it by four, and cursed bags double it.

Tipping or looking into a cursed bag of holding may make items vanish, with a separate 1/13 chance for each item.

Putting dangerous items into bags of holding

Some items should not be put in a bag of holding, or they will make the bag explode – destroying all of its contents along with the bag and damaging the player. These items are as follows:

• Bags of tricks with charges remaining
• Wands of cancellation with charges remaining
• Other bags of holding
• Other bags containing any of the above items, though they have a chance of not exploding if you nest them.

The first two are straightforward to avoid, provided you don't type the wrong letter by mistake; the wand can be trickier. To be safe, do not put any unidentified wands inside the bag, unless you have engrave-tested them and confirmed that they do not make engravings disappear - this rules out cancellation, along with teleportation and make invisible.

It is usually best to avoid carrying more than one bag of holding or any bag of tricks (except perhaps while transporting them to a convenient stash location) - neither is particularly useful to simply carry around, and you can't put one inside your bag of holding by mistake if you don't have it. Many players prefer to leave wands of cancellation at their stash as well, but these can be useful against monsters, so one must balance the increased risk in combat with the risk of making a potential game-ending mistake.

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.

Blowing up a bag of holding in this manner now scatters its contents instead of destroying them - this will break fragile items. If you had put in another bag of holding, its contents are also scattered, unless that bag was inside a non-magical bag, in which case it is destroyed.

Strategy

Bags of holding are useful for carrying large numbers of items, and are an essential part of an ascension kit.

Since a cursed bag of holding can instantly cripple you with its weight and cause you to lose important items, it is important to keep the bag blessed. This also allows you to carry more items.

While magically protecting its contents from breaking when thrown, a bag of holding does not stop them from getting wet - to protect against this, you can apply grease to the bag or place it in a non-cursed oilskin sack to protect it from water damage.

Item management

Due to the risks of losing your most valuable items if your bag is cursed or else explodes, many players also carry a plain sack to store other items. The sack can be used to hold items that are rare or hazardous to a bag of holding - many players name this bag something like "Cancel" or "Don't ever put this in BoH!" and keep wands of cancellation and other precious items such as artifacts or a wand of wishing inside as a safety measure.

You can also store a bag of holding in a sack, which prevents it from being targeted by curse items. However, it will require two turns to take items out of the bag of holding.

Handling cursed bags

If you find a bones pile with a bag of holding, it will probably be cursed and too heavy to lift. If you can still pick it up, then it can be uncursed with a potion of holy water or the scroll or spell of remove curse. Otherwise, the best solution in general is to zap it with a wand of cancellation - the beam will only affect the bag and simply sets its beatitude to uncursed. Be sure to move any wands and tools out of the way beforehand, along with any other desired items that you suspect may be enchanted or charged.

If cancellation is not available and the bag is too heavy to lift, you can #tip the bag - this will still make items vanish, but at least you can get everything else out without being limited by your inventory.

You can also allow a gelatinous cube to eat the bag if one is present: the cube will only eat the container itself, leaving the contents (including organic items) in its inventory, which will land safely on the ground when you kill the cube. Just make sure you can secure all the items before they are damaged - and only do this if you have no need for the bag itself.

Nesting bags of holding

It is possible, though risky, to first put items that would ordinarily cause a bag of holding to explode into sacks or oilskin sacks and then place them inside the bag of holding, without causing an explosion.

In general, two nested bags of holding at most are useful - the payload is limited by your ability to lift the innermost bag, not by the outermost weight, and you risk an explosion every time you add contents.

The chance of an explosion occurring then depends on the amount of nesting:

Number of sacks	Odds of explosion	Success probability
0	1/1	0
1	2/2	0
2	3/4	0.25
3	4/8	0.5
4	5/16	0.6875
5	6/32	0.8125
6	7/64	0.890625
7	8/128	0.9375
8	9/128	0.9296875
n, where n>6	(n+1)/128

If they do not explode, the effect of the two bags will be cumulative, as expected: if both are blessed, any items in the innermost bag will have their weight reduced to about 1/16.

As can be seen in the table above, nesting bags of holding with more than 7 sacks in between makes explosion more likely, so there is no point in using more than 7 sacks.

You may choose to continue to nest the bags of holding further; the chance of success with certain configurations of sacks between the bags of holding is given below:

Number of bags of holding	Sack spacing	Success probability
2	7	0.9375
3	7,7	0.769042...
4	7,7,7	0.512570...
5	7,7,7,7	0.256222...
6	7,6,6,6,7	0.0935839...
7	7,6,5,5,6,7	0.0236287...
...
43	3,2,2, ... ,2	very small

For example, if you use 7 sacks between each of three bags of holding like this (H for bag of holding, s for sack): HsssssssHsssssssH (denoted as "7,7" in the table above), the chance of successful nesting would be 1-(8/128) for the first nesting, and then (1-(8/128)) * (1-(16/128)) for the second nesting; each of the two 'inner' bags of holding put into the outermost bag must pass its own independent roll for the nesting to succeed - this gives the example scenario roughly a 23.1% chance that something will explode.

Some players either consider the 6.25% chance of explosion from nesting to be an acceptable risk, or assume from a test in wizard mode that it is safe. If you are confident you can withstand the explosion, you can risk it before you leave the main dungeon to increase your score or bring specific items to the ascension bar.

History

The bag of holding was introduced in NetHack 3.0.0.

In NetHack 3.4.3 and some variants based on it, Sokoban Level 4a always has a bag of holding as the prize.

Messages

An <object> has vanished!

You applied or #looted a cursed bag of holding, causing a known item(s) to disappear.

You see <object> disappear!

As above, with an unidentified item(s) disappearing.

As you put <object> inside, you are blasted by a magical explosion!

You caused a bag of holding to explode by placing a charged bag of tricks, charged wand of cancellation or another bag of holding inside, destroying both objects and their contents.

Variants

SLASH'EM

In SLASH'EM, you can upgrade an ordinary sack or oilskin sack into a bag of holding. This typically makes the amulet of reflection found at the end of Sokoban a more valuable prize - there is still a 50% chance of each reward.

The Wallet of Perseus is an unaligned artifact bag of holding; the 'naming artifacts' trick is functional in this variant, and naming a bag "The Wallet of Perseus" can distinguish the bag of holding from other bags. Additionally, SLASH'EM has an option, showweight, that explicitly shows the weight your character is carrying - informally identifying bags of holding is trivial with this option turned on.

NetHack brass

In NetHack brass, Sokoban offers a choice between 3 items, with one being a bag of holding.

GruntHack

In GruntHack, causing a bag of holding to explode does not destroy the contents of the bag, but scatters them and the player throughout the dungeon via level teleport.

Sokoban in GruntHack also offers a choice between 3 prizes, with one being a guaranteed bag of holding.

SporkHack

In SporkHack, an exploding bag of holding scatters its contents nearby, rather than destroying them outright - this will still destroy the inserted object, and fragile objects such as potions and mirrors are broken as if they were thrown.

UnNetHack

In UnNetHack, exploding bags of holding react the same as in SporkHack, scattering most of its contents and destroying fragile items.

Sokoban in UnNetHack offers a choice between 3 prizes, with one being a guaranteed bag of holding.

AceHack

In AceHack, inserting a bag of tricks or a wand of cancellation inside a bag of holding will drain them of their charges rather than destroying any items inside - you can still destroy bags of holding by nesting them, but you will receive a confirmation prompt when doing so. This also applies to NetHack 4, a 'successor' variant to AceHack.

NetHack Fourk

In NetHack Fourk, Sokoban now has set rewards for each of the possible maps that can appear as its final floor. Open at the Top, which is essentially a clone of Sokoban level 4a, always has a bag of holding as its prize.

xNetHack

In xNetHack, if a bag of holding explodes, ¹⁄₁₃ of the contents are destroyed along with the bag and inserted item, and the rest are scattered; this destroys fragile items as usual.

EvilHack

In EvilHack, an exploding bag of holding functions similarly to UnNetHack - the inserted item and the bag are destroyed, and most of the contents are scattered, breaking fragile items.

Sokoban in EvilHack offers 3 different type of prize item, and its prize tool has a 50% chance of being a bag of holding. The Bag of the Hesperides is an artifact dragonhide bag of holding similar to the Wallet of Perseus, and can only be obtained at the end of the Ice Queen's Realm.

Encyclopedia entry

"Now, this third handkerchief," Mein Herr proceeded, "has also four edges, which you can trace continuously round and round: all you need do is to join its four edges to the four edges of the opening. The Purse is then complete, and its outer surface--"
"I see!" Lady Muriel eagerly interrupted. "Its outer surface will be continuous with its inner surface! But it will take time. I'll sew it up after tea." She laid aside the bag, and resumed her cup of tea. "But why do you call it Fortunatus's Purse, Mein Herr?"
The dear old man beamed upon her, with a jolly smile, looking more exactly like the Professor than ever. "Don't you see, my child--I should say Miladi? Whatever is inside that Purse, is outside it; and whatever is outside it, is inside it. So you have all the wealth of the world in that leetle Purse!"

[ Sylvie and Bruno Concluded, by Lewis Carroll ]