Name tags are items that can be used to name mobs by right-clicking on them. Name tags are not craftable, so the only way to legitimately obtain them in Survival is to find them inside of dungeon chests or strongholds, through trading, or by fishing.
Name tags must first be renamed with the use of an anvil before being applied to a mob (which, as of 1.8, costs 1 experience level, and on console editions, it costs 5). To use a name tag, simply hold the item and right-click on a mob to name it. Once done, the new name will display above the mob's head in a similar manner to a player's username. Once a mob is named, it can never be un-named, though its name can be replaced via another name tag.
Outside of naming mobs, name tags are useful for preventing mobs from despawning. Once a mob is named, it will remain in the world until it dies, regardless of the time or the player's distance from it. This makes it a great tool for hostile mobs (which can help in curing a zombie villager), which usually despawn during the day, or for neutral mobs and passive mobs, such as horses, in order to save them for a player to use no matter how far away they are or how long ago they were "rendered."
- If a mob is named "Dinnerbone" or "Grumm", it will be flipped upside down. This is an easter egg for Nathan Adams, a developer with the same Minecraft nickname.
- Players on iOS and Android can flip themselves upside-down in-game by changing their usernames to "Dinnerbone" or "Grumm". This only works if you sign out of your account and in versions 1.1.0 and above.
- If a sheep is named "jeb_", its wool will cycle through the colors of the rainbow. It will continuously change color through all the types of wool, and will not stop unless it's either killed or renamed. However, this effect is purely aesthetic. If it's killed or sheared, it will drop the color of its original wool.
- If a rabbit is named "Toast", its texture will be changed to a black and white fur pattern, similar to the real-life Dutch rabbit. This is done in honor of a Minecraft user's girlfriend's lost rabbit.
- If a vindicator is named "Johnny", it will be unconditionally aggressive to any mobs and players that are near it, except for any type of Illagers and ghasts. This is a reference to the film The Shining and Hungry Shark games.
- Names of tagged mobs are visible within 4 blocks.
- If the Wither is named using a name tag, its boss health bar will display the new name.
- The killer bunny mob used to spawn with a name above it that said, "The Killer Bunny."
- If curse words are written on a name tag, it will censor them.
- A name tag can be traded for 20 emeralds at the librarian's master level.
- Any mob using a name tag will not despawn.
- Name tags do not grant immunity, as any mob currently using one can still be killed, but will not naturally despawn on its own.