Parts of this entry were adapted from the NetHack Elbereth FAQ by Kate Nepveu
Elbereth (also called the E-word) is, in the writings of J.R.R. Tolkien, the name of a divine being worshipped by elves. Engraving her name on a square prevents most monsters from attacking you while you are on that square. Use of Elbereth is a key survival strategy for new players and/or characters, the difference between death and survival in many games. It is therefore worthwhile to study this entry and learn all the ins and outs of the use of Elbereth.
A monster that respects Elbereth will not attack you in melee combat (hand to hand) while you are standing on it, and will not generally move onto a square that contains an active engraving of Elbereth. This is therefore a popular way to protect stashes. Note that there must be something, like you or any dropped object, in the same square with Elbereth for it to be active and have effect--an engraving on an otherwise bare square will not deter monsters.
Pets will also benefit from Elbereth if you engrave it for them.
Most monsters in the game respect Elbereth; the exceptions are generally human or human-like, and are noted below.
No monster represented by an @ will respect the word, and neither will any capital A, minotaurs, or the Riders. Keystone Kops and their officers, while human for many game purposes, will respect Elbereth, but only if you are standing on it. Shapechangers will respect it while they are in a form that otherwise would, and will not respect it while in a form that otherwise would not (such as a werecreature in human form). Certain monsters, such as shopkeepers, guards, high priests, and The Wizard of Yendor will never respect it, even if they are polymorphed into a form that otherwise would.
Any tame or peaceful monster will not respect Elbereth. This is obviously not a problem in terms of avoiding attacks, as these monsters generally won't attack you. But it does complicate using Elbereth to protect a stash, as pets or peaceful monsters will freely move onto your stash square, and possibly erode the engraving. It also means that if you plan on using conflict to dispose of a group of monsters while waiting on an Elbereth square, you may have to endure attacks from any pets you have with you.
Additionally, engraving Elbereth on the up staircase and dropping an item on it will not prevent teleporting monsters from escaping to the up staircase square. This is a partial exception to the rules, to keep it from being too easy to defeat these monsters.
Take special care to note what Elbereth will not do. It will not protect you from any missile or spell attacks, or anything else that allows a monster to inflict damage from a distance, such as a dragon's breath attack. It will not make monsters peaceful, or protect anything on another square (such as your pet). Hostile monsters will still want to kill you, and will do anything they will ordinarily do to harm you, except attack you hand-to-hand.
Partial exceptions when Elbereth will still protect you from non-melee are: No monster already fleeing from you due to Elbereth can use its ranged attacks, absolutely while adjacent and at least with much smaller likelihood if not. Any dragon will choose melee over its breath weapon if it is adjacent to you, and if it cannot engage you because of Elbereth, it will not attack you at all. Therefore, a popular strategy is to confine monsters next to you using active Elbereth squares, e. g. while sacrificing or making dragon scale mail.
Elbereth will not stop working if you attack monsters while standing on it, although your actions may cause the engraving to erode (see below). It is thus popular for missile-wielders and spellcasters to fire away at their opponents while protected by Elbereth. Considering this, a good use of Elbereth, especially when surrounded, is to engrave it on the floor and wait for your HP to increase. Once they're good and high, throw a few attacks about. Once monsters realize that you are no longer protected, engrave it again. This can be very useful for level grinding.
Elbereth is case-insensitive, and will work even if it is surrounded by other writing, so "Aelberethgilthoniel" would be effective. Engraving "Elbereth" as written, with capital "E," however, will exercise wisdom, so it is most beneficial to do it this way. You can use Elbereth while engrave-testing wands for this added bonus.
Elbereth stops working when it degrades into a different word. If you are writing in the dust ([E] [-]), you might want to write it several times. (Copy-paste: "E-y Elbereth") The immediate result of one test was "ElberLth ElbereGh ElVereth Ylbereth Elbeheth Elb;reth Elbereth Elbereth tlbere#h".
Chances of Engraving
As with any engraving, you are not guaranteed to engrave perfectly if you are impaired or writing in the dust. If you are writing in the dust (with fingers, a wand, a soft gem, etc.) or are scrawling in blood, your chances of messing up each letter add up to a ((0.96+0.04*2/94)8) or ~72.7% on each attempt, as each of the eight letters in Elbereth must be engraved or "mis"-engraved correctly for the word to have power. "ElberethElbereth" raises the chance to 92.5%. It is entirely possible to require three, four, or even more attempts to get a correct "Elbereth" written in the dust, so you must not wait until you are one turn from death to get this done! If you can see, you can inspect your work with the "look" command, ([:]). You will also know it is working if you see the message, "The (monster) turns to flee!"
Speed and Quality
Engraving techniques may be classed as fast (fingers, wand, athame) or slow (other weapons, hard gems) (see Engraving#Speed for details). With a fast method, you can engrave up to 9 characters (enough for one Elbereth) immediately; this takes one move, and has immediate effect - affected monsters will not get another attack (if the engrave succeeds). This is almost always the preferred way to use Elbereth.
Alternatively, you can engrave between 10 and 19 characters (enough for 2 Elbereths) per game turn with a fast method, or 1 character per game turn with a slow method. This takes the whole turn to finish, and is not effective until the turn is over, so monsters typically get an attack during that time (unless you are on a free turn due to being fast or very fast). And, while doing this, any existing engraving is obscured, so any Elbereths that you have already written are ineffective during this turn.
If you engrave multiple characters with a slow method, or more than 19 characters with a fast method, it takes more than 1 turn. Throughout these turns the engraving offers no protection and you are 'helpless': unlike reading a spellbook or eating a food ration, you won't be interrupted if something attacks you. No monster will respect Elbereth until your entire engraving is finished.
So you usually want to use a fast method to engrave and write a single Elbereth. If you wish to engrave multiple Elbereths as a precaution against erosion, engrave them one at a time, adding to the current engraving each time. A fast method, even writing in the dust, is almost always preferable over a slow one.
Note that you do not need to add a blank space between individual words - engraving "ElberethElbereth" is functionally equivalent to "Elbereth Elbereth" and one character less.
Engravings may be classified as permanent (will not degrade), semi-permanent (will degrade slowly), or temporary (will degrade very quickly).
For a permanent Elbereth, use a wand of fire or wand of lightning to burn it. The wand of lightning can blind you, but that is an acceptable risk during an emergency. (Note that the blindness takes effect after the engraving is completed--you will not increase your risk of misengraving through blindness.) Otherwise, unless you can easily cure blindness or protect your eyes, avoid any engraving with the wand of lightning. Permanent Elbereths are ideally suited for protecting stashes, since a stash needs to last a long time. Permanent Elbereths are also useful in combat situations, but because they always require a wand charge it is best to save them for difficult situations instead of using them routinely. Permanent Elbereths will not erode from being stood on or walked over, but can be eliminated through techniques such as engraving over them or engraving with a wand of polymorph.
You can engrave a fast semi-permanent Elbereth using a non-cursed athame, a wand of digging or a charged magic marker (consuming four charges). Athames are the best way to engrave Elbereth in routine combat as they engrave semi-permanently and are not reliant on charges. Unfortunately, athames are difficult to find. They are never randomly generated, so you need to pick one up from a Master lich's inventory, get gifted Magicbane from your god or wish for one. Wizards' first sacrifice gift is Magicbane so they have the easiest time getting hold of an athame.
Semi-permanent Elbereths will erode over time as they are walked over or stood upon, but not nearly as quickly as will temporary (finger) engravings. See Engraving#Durability.
You can make a temporary "engraving" (actually just drawing in the dust on the floor, or writing in blood if you are polymorphed into a vampire) with your fingers by responding "-" when asked what to engrave with, or you can use a soft gemstone, or any wand other than fire, lightning, or digging (certain wands may have undesirable effects on the engraving itself, such as polymorphing it). This is fast, but subject to the 1/25 chance of mis-engraving per letter, and any movement, such as fighting or throwing missiles, will damage the engraving. Even standing still on the engraving will eventually degrade it, as no one stands perfectly still. However, one can levitate after engraving to keep the engraving from being eroded (if it is not already).
Slow engraving methods
Hard gemstones, any ring with a hard gemstone set in it, and bladed weapons (other than athames), can be used to engrave semi-permanent Elbereths, but these techniques are slow and will make weapons dull.
If you want to engrave with a slow method, a) don't, b) if you really must, do it one letter at a time. Yes it is a pain, but engraving more than one character at a time is dangerous due to being rendered helpless while engraving.
Another drawback of slow engraving is that, if you only have slow ways to do a semi-permanent Elbereth, you have no safe way to repair it once it is eroded. You can't add a fast dust Elbereth over the top; and slow engraving obscures any Elbereth already on the ground, so you can't add more free semi-permanent Elbereths in safety. So you are then forced to use up a charge for a permanent Elbereth, or a wand of digging to update your semi-permanent Elbereth. Hence slow Elbereths are very unsuitable for combat situations.
A funny wrinkle in the engraving rules means that a ordinary +0 weapon will not be able to engrave the entire word "Elbereth" at one go--you will only get as far as "Elberet" before the weapon reaches -3 and is too dull for engraving. It will work, however, if you engrave first "Elb" (for minus one to the weapon), then add "ereth" to the current engraving (for an additional minus two).
Elbereth and levitation
If you levitate over an Elbereth, the word will never degrade as long as you are levitating over the square, no matter what you do while levitating over it. Characters who can levitate may want to take advantage of this by engraving Elbereth and then levitating over it while fighting off large numbers of monsters. Note, however, that during an emergency, it is usually preferable to burn a permanent Elbereth using a wand, assuming that you have enough wand charges to spare.
Don't blind monsters!
A blinded monster that can ordinarily see will not respect Elbereth while it is blind. Don't use a camera, for instance, while you are hiding behind the power of Elbereth. Blind monsters can not read the word anymore and will attack you. Note that unseeing monsters, such as gelatinous cubes, which do not have sight in the first place, will respect Elbereth. Go figure.
Strategy: other uses
Besides protecting you from melee during extended fights or while firing missiles and spells, protecting your stash, and keeping dragons from using their breath weapon as detailed above, there are some less straightforward uses.
Especially if you are low on armor or a weak fighter, you might want to partition the dungeon with active Elbereth squares in every door or empty doorway you traverse. This will keep monsters generated out of sight from teaming up on you. A gold piece is perfect to activate Elbereth, since gold is abundant and lightweight. If you have pets, cursed objects are better, such as darts and arrows.
Wraith luring is much easier if you make an artificial corridor of Elbereth squares to the stairs. A similar case is directing pudding flow if you farm.
If you do altar work, you might want to keep monsters next to you with a boulder fort and burn Elbereth everywhere to protect your pets and to keep giants from picking up the boulders.
Elbereth will make engulfing monsters expel you. If you can take the hit and do not have a sure-fire method, it is often better to start writing a sequence of several Elbereth in the dust because you will not be allowed to retry once you are inside.
Sometimes, is a worthwhile idea to prepare a semi-permanent Elbereth square in advance as means of escape, e. g. some corner in Sokoban for pacifists without a pet.
... Even as they stepped over the threshold a single clear
voice rose in song.
A Elbereth Gilthoniel,
silivren penna miriel
o menel aglar elenath!
o galadhremmin ennorath,
Fanuilos, le linnathon
nef aear, si nef aearon!
Frodo halted for a moment, looking back. Elrond was in his
chair and the fire was on his face like summer-light upon the
trees. Near him sat the Lady Arwen. [...]
He stood still enchanted, while the sweet syllables of the
elvish song fell like clear jewels of blended word and melody.
"It is a song to Elbereth," said Bilbo. "They will sing that,
and other songs of the Blessed Realm, many times tonight.
Elbereth may not be present in every installation of NetHack, because it can be compiled out of the game. You can use the #version command to check for this.
You can burn Elbereth into the floor with a lit lightsaber as if using a wand of fire or lightning.
A warning to players of the NetHack brass variant: Avoid engraving Elbereth with wands. While vanilla uses 1 wand charge per engraving, NetHack brass can consume extra charges. An engraving with a wand of fire, for example, costs the usual 1 charge engraving with a wand, an extra 1 charge because the wand is a wand of fire, plus 1 charge for each letter engraved. To burn Elbereth successfully, you would need 10 charges in your wand of fire; you probably do not have them.
In SporkHack, Elbereth doesn't always work. On weaker monsters, it works most of the time, but especially against higher-level monsters it's no longer perfect protection. That said, it works often enough that it's almost certainly worth using everywhere that it's worth using in vanilla or SLASH'EM.