Eye of Ender

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

Locating strongholds
To locate stronghold s (and the end portals they house):
 * Pressing while holding an eye of ender causes 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.
 * $$, the eye leads to near the spiral staircase that was the first room generated in the stronghold.
 * $$, eye of ender signal leads to 5 crossing room that was the second room generated in stronghold.
 * $$, a thrown eye leads 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 travels downward, 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 player can throw the eye an average of five times before it shatters.
 * The Eye of Ender's flying function works only 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 that locates strongholds $$. View the project Readme on GitHub for usage instructions.

Activating end portals
Once an end portal is found, eyes of ender are required 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 a one out of 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 that 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.