Eye of Ender

An eye of ender (or ender eye) is a craftable item used to locate strongholds and activate the end portals within them.

Locating strongholds
To locate strongholds (and the end portals they house):
 * Pressing while holding an eye of ender will cause it to fly approximately 12 meters in the direction of the nearest stronghold, traveling through any blocks necessary, and leave a trail of purple particles in its wake, the same particle effect used for ender chests.
 * In Java Edition, the eye will lead near the spiral staircase that was the first room generated in the stronghold.
 * In Bedrock Edition, eye of ender signal will lead to 5 crossing room that was the second room generated in stronghold.
 * In the Legacy Console Editions, a thrown eye will lead to a stronghold, but not exactly to an end portal.
 * While far away from an end portal, the ender eye always travels upwards to offer an easily-visible indication of the horizontal direction the player must travel.
 * When the player gets close to the stronghold, the eye floats in a more precise direction that takes the y-axis into account. This often means the eye will travel downwards, to indicate the player is above a stronghold and must mine downwards.
 * After two or three seconds of travel, the eye floats in the air briefly, then either falls (becoming collectable again), or shatters in mid-air. The Eye has a 20% chance of shattering.
 * The Eye of Ender's flying function only works in the Overworld. It does nothing in the Nether, the End, or in worlds with no strongholds.

Also, see minecraft-stronghold-locator, a web tool which can help you locate strongholds by visualizing what the eyes of ender are telling you for the Java Edition. View the project Readme on GitHub for usage instructions.

But be careful they can blow up if you look at them too much.

Activating end portals
Once an end portal is found, eyes of ender will also be required in order to activate it. End portals require a total of 12 eyes of ender in order to activate, though each individual frame block has a 10% chance of containing an eye of ender when generated. Eyes can be placed in empty End portal frames by pressing on them until the entire ring of 12 is filled, thereby activating the Portal. Due to the fact that there is a 10% chance of each individual End portal frame having an Eye in it, there is about a 1 in one trillion chance of every frame having an Eye in it thereby activating the portal even if you have no eyes of ender.

Entity data
The purple particles left by ender eyes have entity data which define various properties of the entity.

Trivia

 * When in third person view, the eyes of ender fly out from the player's feet instead of their hand.
 * The player cannot throw eyes of ender in the Nether, the End, or Customized and Superflat worlds that do not have stronghold generation selected.