Steps on how to not fail on MCP:

Decompiling Edit

  1. Go to, and download the zip for the version you want to decompile and extract the zip.
  2. Run decompile.bat (in the folder where you extracted it), and wait until its done. Do not close it until it says "Press any key to continue..."!!
  3. Install Eclipse, and select the eclipse folder in the folder where you extracted MCP. Now you are done with decompiling.

Missing Library/Natives Edit

Some jars (most commonly the realms jar) gets updates regularly to fix bugs/exploits. Since MCP always copies the latest version of the jar as specified by the launcher, this sometimes breaks the libraries. In order to fix this, simply find and select the latest version of the jar. The same goes for 1.X.jar and the natives if you using a custom MCP (e.g. MCP 1.11 with 1.11.2 mappings).

For natives, here's how to fix:

First go to your libraries and the 1.X.jar that is attached. Click it and click the expand button (>) on the left side.

Go to native library location and click edit. What is extremely annoying is that Eclipse doesn't warn/error when the native library is not found, causing you to think you placed the library when you really didn't.

Click "Workspace". It should be jars/libraries/1.X/1.X natives where 1.X is the version.

Click Ok. The warning that the folder doesn't exist should be gone.

Recompiling Edit

  1. Run recompile.bat, again waiting for it to be completely done. Do not run reobfuscate.bat until you run this one! Your changes will not appear if you did so.
  2. Run reobfuscate.bat, and your changed files will be at reobf/minecraft.

Using Mappings Without a Release Edit

(needs a better title)

As you may or may not have heard, the MCP mappings for 1.11.2 are already out, but there was no MCP release for it. Here's how to use the mappings for 1.11.2 for MCP 9.35 (and any other version)

First, download the mappings you want. The mappings are located at

where 1.X is your version. For example, 1.11.2 mappings would be at

If there are no mappings at your desired version (e.g., that means that no mappings have been made. Your best bet is to try a nearby version (1.8 or 1.8.8)

Note: It is also known that 1.8.9 mappings are broken. There is no fix for it.

Next, delete everything in the conf folder where you extracted MCP except for mcp.cfg and version.cfg.

Copy what you have downloaded into the conf folder.

Next, go into version.cfg, and change the version to the version you want to decompile.

You are now done!