Experience



Experience points were added to Minecraft during the first part of the Adventure Update. They were originally revealed by Jeb during an interview. Experience can be obtained by gathering Experience Orbs from defeated mobs and players.

Behaviour
Gathering experience points increases the player's experience level by gradually filling a bar on the bottom of the screen until a new level is achieved when the bar is full. Each level up will potentially reward the player with Skill Points, which Notch has said may be used for buying things such as increased jump height and increased maximum health.

Currently, as of 1.0, there is a bug where gathering many XP orbs at once allows you to gain a number of XP levels equal to the number of orbs collected divided by the amount of required to gain the next level. Example: Gaining 350 experience while at level 0 will raise the player to level 50, since 7 XP is required to go from level 0 to level 1. This is most easily seen using the /XP  command on a server.

Jeb has stated on Twitter that Experience Orbs will not drop unless the creature is killed by a player, rendering grinders useless for farming experience (although grinders can be converted to funnel monsters to an easily player kill-able location to grind experience).

When the player dies, they only drop half of their experience as orbs, rounded down to the nearest point. The other half vanishes.

Mobs will drop a random number of orbs, and the orbs can have different values. However, the total value will always remain within these values, regardless of difficulty setting:



Leveling Up


For any given level, the experience, E, required to achieve the next level n+1 from the current level, n is: E = (n + 1) * 7

The experience, E, required to achieve level n from level 0 is: E = 3.5n * (n + 1)

Also, to reach level x from level n, one would need E experience:

E = 3.5(x(x + 1) - n(n + 1))

History
Jeb released a picture of the 1.8 GUI list, which shows the experience bar, among other things.

When first added in Beta 1.8, there was no measurable benefit to gaining Experience Orbs and levels.

As of 1.9 prerelease 3, experience levels are indicated by a number above the experience bar, which increases by one every time the bar is filled.

The ability to spend experience levels for Enchanting items was added in 1.9 Pre-release 3, and enchantment was enabled in SMP in 1.9 Pre-release 4.

Trivia

 * In Beta 1.8 Pre-release 1, when the player died, they dropped all of their experience orbs individually. This created a problem with retrieval of drops if the player had accumulated a large sum of experience, due to the extremely large amount of orb items created at the specific point. On SMP servers, this could be enough to even crash a server.
 * In Beta 1.9 Pre-release 1, the player gained Experience from jumping. This was part of code left in by Jeb for testing Experience.
 * Experience levels have an exponential scaling, meaning that it becomes progressively harder to achieve higher and higher levels.
 * Experience orbs will drop from a mob if it dies from fall damage as a result of the player knocking it off a cliff.
 * To reach level 50, which is the amount of skill points required to purchase the highest type of enchantment, one would need to gather 8925 experience by defeating 1785 hostile mobs.
 * Experience orbs will despawn if a player sleeps before collecting them. This means if you die at night and sleep before collecting your items, the orbs will disappear when you wake up.
 * Using enchantments does not decrease your score (which is shown on death).
 * In the resources folder of Minecraft, there appears to be a unused sound of leveling up. It cannot be heard in gameplay.

Bugs

 * When a 1.9 Pre-release 2 world is opened on a 1.9 Pre-release 3 version of Minecraft, the player is given a large amount of experience and the skill bar will look strange. Skillbarbug.png
 * In Beta 1.8, if the player dies with an large amount of experience, and returns to collect it after respawning, sometimes (usually if FPS drop below 10) the experience orbs will continuously swirl around them. The experience points count on the bar, but the animation continues to loop.  The only known way to fix this bug is disconnecting then reconnecting.
 * In Beta 1.9 Pre-release 4, Enchanting only consumes experience levels, not the experience itself. So, if the player spends 10 points on an enchantment, and then dies, the points can be regained after respawning.
 * In 1.0 release, gathering many XP orbs at once allows you to gain a number of XP levels equal to the number of orbs collected divided by the amount of orbs required to gain the next level.
 * In Minecraft 1.0.0, Experience is not always rewarded after killing an animal/mob/player, this may be due to effects such as "Fire Effect" for swords which do additional damage and that damage may not be attributed to you. Animals/mobs should give experience 100% of the time if you use a standard sword and the killing blow is yours.