Explore mode is a special game mode, intended for players still learning the basics, which grants several advantages to the player.
Public servers like nethack.alt.org tend to disable it. It can be invoked in a new game by starting NetHack with the -X option, or in an existing game by pressing X. If you start a new character in explore mode, your character will have a pre-identified uncursed (0:3) wand of wishing, in addition to their standard starting inventory.
Inputting ctrl + x while in explore mode, will not only show your basic attributes, but also your current ones, as if you had used an uncursed wand or potion of enlightenment. Once entered, a character may not leave explore mode. When an explore mode game ends, the score is not saved to the record file.
The most prominent feature of explore mode allows you to refuse death at will. When your character would die, you are prompted as follows:
Type n, and you receive the message "Okay, so you don't die.", and the game continues much as though you were wearing an amulet of life saving (if you *were* wearing an "oLS, it will be consumed as normal and you won't receive the prompt). You can refuse any sort of death short of a trickery, even ones that standard life saving won't protect you from.
If you refuse death from brainlessness, your intelligence is arbitrarily set to 5, with the message "You feel like a scarecrow.". If you refuse death from self-genocide, you survive as the last of your race or role, and trying to genocide the same race or role again will fail, except through the uncursed scroll while confused. If you refuse death from levelporting to level 0, it's as though the teleport never happened.
Explore mode also gives you the option to keep your old save file when you restore a game. This allows you to have a single save slot as in many other games, that you can use to undo a sequence of play to experiment with the results of alternative strategies without having to start a new game and get to the unusual situation you wish to explore. (Note that, if available, wizard mode may be even more powerful for this sort of exploration.)
Do you want to keep the save file? [yn] (n)
Explore mode has some value for players who install their distro's NetHack binaries on a Unix system, and lack the correct username to enter wizard mode. The main obstacle for these players is the bother of either creating a user account with the correct name, or compiling NetHack from source code. These players can use the explore mode's wand of wishing to play with specific objects.
Sometimes one remarks that the X key, which changes a normal game to explore mode, may save their hero from an impending death so that they can continue their game.
Players in explore mode may develop abnormal strategies. For example, instead of dealing with a soldier ant in an appropriate way, an explore mode player might just melee it, ignoring how many deaths this takes. Then they repeat this process with the next difficult monster, dying hundreds of times in the same game.