Crashes are unexpected shut downs of Minecraft. When Minecraft crashes, it typically closes immediately, though it may show an error report marking the location of the exception which caused the crash. A sign of a crash is a "Saving chunks" screen. The most common cause of crashes are mods and preexisting bugs. Attempting to modify the files of Minecraft or individual worlds, even with advanced editors, can also cause crashes. Crashes can also be caused by bugs in the game (e.g.: before the beta 1.6.5 update, shift-clicking an item into a full chest would crash the game.) Crashes can sometimes cause the corruption of save files if the player is not careful enough. Because of this, it is highly recommended that you regularly keep a copy of your save folder (located in the %appdata%/.minecraft directory on Windows systems or ~/.minecraft/ in linux), to reduce your losses should a world become corrupted as a result of a crash.
Crashes used to have an error report but that feature has been removed. Yet sometimes an error report can quickly flash right before the game closes. Minecraft occasionally will do this on startup, except it stays there, not allowing you to play the game.
 Causes of crashes
Crashes can easily occur due to mod conflicts, or buggy mods. If you've installed several mods, try renaming the "bin" directory in the Minecraft folder, then start Minecraft (Or replace your current minecraft.jar with a clean minecraft.jar from either a clean backup, download a jar file from the internet or force update the game should cause you to get a new clean jar file.). A new bin folder will be created. Now install each mod you desire one at a time, starting Minecraft and assuring that there is no crashing for each mod. Once the crashing starts occurring again, the last mod installed is likely the problem, or another mod simply does not work with it. Either way, either remove the mod you determined to be causing problems, or repeat the first step, except without installing the problematic mod.
 Hardware problems
Problems with your computer's hardware can also easily cause crashing, or buggy behavior. If this is the case, it's likely you're experiencing problems in other, unrelated games as well. If Minecraft is the only game experiencing issues, then it is unlikely to be a hardware issue.
If you are indeed experiencing crashing or visual corruption in other games as well, the first thing to check is whether your computer's vents are blocked, or clogged with dust (which inevitably occurs over time). Dust or vent/fan blockages can cause overheating, which may not be severe enough to cause problems during normal computer use, but during more intensive activities such as gaming, the temperature may spike. If you're using a laptop, make sure any vents on its sides or bottom are neither blocked or filled with dust. For a desktop, check obvious fan locations for blockages, and use a flashlight to peer inside the case. If there is lots of dust, or any internal fans appear to not be spinning, you should either take your computer to a repair shop for a "tune-up" (mention that you suspect there is overheating problems), which you will have to pay for, or read a few tutorials online related to computer cleaning (note that a computer's internal components are highly sensitive to damage from ESD (Electrostatic Discharge, basically a static shock), so it would not be difficult for you to accidentally damage your computer).
If your computer appears to not be suffering from overheating related issues, another cause of game crashing could be damaged components, especially either the RAM, or the video card. If the problem just recently started occurring, and you have not recently installed any major updates or software such as Anti-Virus suites, you may want to take your computer to a shop to have it tested, or you can do it yourself using tools such as "memtest86+", "Furmark", etc. (however these tools tend to require a medium to large amount of computer knowledge).
It should be noted that even if your computer meets the basic system requirements of Minecraft, there is a possibility that your hardware might have unique issues, one being the use of Intel GMA (Graphics Media Accelerator) cards, known for issues with OpenGL.
Though unlikely, unrelated software can conceivably cause crashing in games such as Minecraft. The most likely candidates are User Account Control (Windows Vista, 7 and 8), Gatekeeper (Mac OS X Lion and Mountain Lion), various types of Anti-Malware (i.e. Anti-Virus, Anti-Spyware, Firewall, etc.) software, which could either consume enough system resources to choke other resource hungry applications, or could cause issues as a result of their "Heuristic" real-time scanning. If you recently installed an application such as AV software, try disabling it. If Minecraft stops crashing, you know the AV program is the perpetrator. You can either remove it (not recommended for security reasons), or configure it to ignore Minecraft's folder and executable. If you're unsure of how to, look up some tutorials on the Internet. Another certain crash is to set all the files in the .minecraft folder to read-only.
 Large operations
Doing large, potentially groundbreaking operations like activating a full-face piston head will generate a lot of process and crash the game
 Manual initialization
You can also trigger a crash manually by holding F3 and C. This is used for debugging, and is the safest possible crash. On some computers, pressing fn key will enable the F3 key.
 Witty comments
Witty comments are phrases shown at the top of crash reports generated using the process shown earlier in this article. They do not show on crash screens and are similar in nature to splashes. They can be changed by changing your minecraft.jar .class files. They get selected using the system time in nanoseconds.
|Who set us up the TNT?||A snowclone of "Somebody set up us the bomb" from a badly translated English version of the 1991 game Zero Wing.|
|Everything's going to plan. No, really, that was supposed to happen.|
|Uh... Did I do that?|
|Why did you do that?|
|I feel sad now :(|
|I'm sorry, Dave.||Part of the famous quote "I'm sorry, Dave. I'm afraid I can't do that." from the movie 2001: A Space Odyssey.|
|I let you down. Sorry :(|
|On the bright side, I bought you a teddy bear!|
|Daisy, daisy...||Also from the movie 2001: A Space Odyssey when HAL started singing.|
|Oh - I know what I did wrong!||A cross-reference to the "I just don't know what went wrong :(" witty comment.|
|Hey, that tickles! Hehehe!|
|I blame Dinnerbone.||Dinnerbone is a Mojangsta.|
|You should try our sister game, Minceraft!||References the easter egg in Minecraft where the title screen has a rare chance to rearrange the C and E in the title.|
|Don't be sad. I'll do better next time, I promise!|
|Don't be sad, have a hug! <3|
|I just don't know what went wrong :(||A cross-reference to the "Oh - I know what I did wrong!" witty comment.|
|Shall we play a game?||Quote from the movie WarGames when the character David Lightman first contacts the computer Joshua.|
|Quite honestly, I wouldn't worry myself about that.||Another quote from from 2001: A Space Odyssey. HAL's answer to Frank: asking: Well of course I know all the wonderful achievements of the 9000 series, but, uh, are you certain there has never been any case of even the most insignificant computer error?|
|I bet Cylons wouldn't have this problem.||The Cylons are a recurring part of the show Battlestar Galactica.|
|Surprise! Haha. Well, this is awkward.|
|Would you like a cupcake?|
|Hi. I'm Minecraft, and I'm a crashaholic.||The common introduction in Alcoholic's Anonymous meetings (and other addiction help groups) where the current speaker starts off with "Hi, my name is _____ and I'm an alcoholic".|
|This doesn't make any sense!|
|Why is it breaking :(|
|Don't do that.|
|Ouch. That hurt :(|
|This is a token for 1 free hug. Redeem at your nearest Mojangsta: [~~HUG~~]||From the game 'Little Inferno' where you get a coupon for one free hug from Miss Nancy.|
|There are four lights!||From Season 6, Episode 11 of the show Star Trek: The Next Generation where Capt. Jean-Luc Picard is captured and tortured by Cardassians, which itself is a reference to real life torture techniques.|
|Witty comment unavailable :(||Displayed if a comment fails to get selected, which is rare due to the way the comments are coded. Ironically, this is a witty comment.|