Mods/Cheating

Hacking is altering software in order to make it work in a way not originally intended. This is not be confused with 'Cracking' or Black Hat hacking - the process of defeating of security devices in computer networks or software copy protection. For more on the difference between types of hacking, see this article.

In Minecraft, hacking refers to using a memory editor in order to alter the variables which the Minecraft Java runtime, or standalone application is storing on your computer. This allows you to do virtually anything, including access blocks not usually available (such as a Mob Spawner).

Beta
No known methods for hacking server-side inventory, previous method will only work in single player.

Alpha

 * 1) Open Minecraft and start a new game or load a saved game.
 * 2) Open Cheat Engine (Windows) or Game Conqueror (Linux).
 * 3) Select process 'javaw.exe' near the bottom ('java' for Linux).
 * 4) Get at least 3 of some block type in your quick slot.
 * 5) Start a new search and search for that quantity
 * 6) Drop an item (Q).
 * 7) Search for the new value.
 * 8) Drop another (or pickup the old one, doesn't matter).
 * 9) Search for the new value. You should only have a few now. Repeat until you only have ONE entry.
 * 10) Double click to add entry.
 * 11) In the bottom pane, right click and choose 'Browse this memory region'.
 * 12) Exactly 8 bytes to the right of the block's quantity is the block's TYPE. Compare with the hex values found here
 * 13) To change the type, copy the DECIMAL value from the data values page, double click on the type in the memory viewer, select 2 bytes, and paste. You can do this for items (e.g. Ingots) as well as blocks

Here is a video going through the process

Classic

 * 1) Pull out Cheat engine or another memory editor.
 * 2) From the PROCESSES List, select 'java.exe' or 'javaw.exe' (Please note: If you have downloaded the standalone, select 'Minecraft.exe' from the list instead.)
 * 3) In minecraft, make sure you have the first block in your UI as stone.
 * 4) Scan for the exact value 1
 * 5) Go to minecraft and change the first block in the UI to cobblestone.
 * 6) Scan for the exact value 4
 * 7) Go to minecraft and change the first block back to stone
 * 8) Repeat step 4
 * 9) This should yield one or two addresses. Pick one (or both) and change the value to one of the following material values from this list.

Health
Even with peaceful mode set, it is easy to fall into lava and die, losing all your hard earned ores in the process. Luckily, it is very easy to hack your health to become truly invulnerable.

Method

 * 1) Open Minecraft.
 * 2) Open Cheat Engine and select javaw.exe.
 * 3) Get your number of hearts, and double it, adding one if you have a half heart (full hearts = 20), and start a new search in CE with this value.
 * 4) Get hurt a bit, or heal a bit, and recalculated your HP. Enter this value for the next search.
 * 5) Repeat until one value remains. Double click to add.
 * 6) Either set to a very high value, or set to 20 and freeze.
 * 7) Enjoy invulnerability.

Here is a video going through the process

NOTE: If you freeze your value, do not enter/leave The Nether, this will move the address where you HP is stored, possibly leading to data corruption and crashed games. Also, you won't be invulnerable again. You can re do the above hack WHILE in The Nether, though, and it works fine.

Consequences
Trying to do this can result you in getting banned/kick/ipbanned in multiplayer servers, though the server will know when you're cheating/hacking. It will display "Cheat detected: Tile type" and will reset everything back to normal, so it only works in Single player. It should be noted that hacking is only appropriate in single player mode, and attempting it on a multiplayer server can result in the software kicking you from the server.

Cube of destruction (CoD)
A cube of destruction is actually a n*n*n cube of tnt, that has been frozen on the TNT state and will never change back to air until the JVM changes block addresses.
 * 1) Open minecraft and load/start a new game.
 * 2) Collect a few of any block type (dirt recommended) and place your cube (any size, any shape).
 * 3) Open Cheat Engine and select javaw.exe at the bottom of the process list.
 * 4) Select size 'Byte'
 * 5) Search for the value of the type of block you used (3 for dirt, find other data values if you used another block type).
 * 6) Destroy the cube.
 * 7) Return to CE, and search again for value '0'.
 * 8) Reconstruct the cube at the same exact spot.
 * 9) Search again for the block's value.
 * 10) Repeat placing, filtering for block type, destroying, and filtering for 0 until only a few items are on the list (i.e. 8 for a 2*2*2 cube), then select the values and click the red arrow.
 * 11) Set the values to 46, and then freeze.
 * 12) In game, whack a few of the TNT and run.
 * 13) You will die unless you hacked your health. Before respawning, un-freeze the values, and respawn to see the damage.

There is a video showing the process here.