Obfuscation maps are ProGuard mappings from old (original) names to new (obfuscated) names for classes and class members that have been renamed. They have been exported in the client.json for every snapshot and release available in the Launcher since 19w36a, and the client.json for 1.14.4 has been updated slightly after 19w36a's release to include obfuscation maps as well.
Dinnerbone and Adrian Östergård have suggested that the obfuscation maps may make modding easier. Searge has implied that the obfuscation maps can replace certain third-party programs such as the Mod Coder Pack.
On August 12th, 2020, Dinnerbone states that modding projects can switch to official Mojang names provided in the obfuscation maps.
The obfuscation maps include enough information to deobfuscate Minecraft for decompilation. A tutorial is available.
According to the License, such decompiled source code can only be distributed in a modified version or part of a larger project. This was changed from being available only for internal purposes before August 14th, 2020.
Every obfuscation map file starts with a line indicating the license of the maps.
This current license has been in use since 21w03a.
# (c) 2020 Microsoft Corporation. These mappings are provided "as-is" and you bear the risk of using them. You may copy and use the mappings for development purposes, but you may not redistribute the mappings complete and unmodified. Microsoft makes no warranties, express or implied, with respect to the mappings provided here. Use and modification of this document or the source code (in any form) of Minecraft: Java Edition is governed by the Minecraft End User License Agreement available at https://account.mojang.com/documents/minecraft_eula.
Versions prior to 21w03a have a slightly different license.
# (c) 2020 Microsoft Corporation. All rights reserved. These mappings are provided "as-is" and you bear the risk of using them. You may copy and use the mappings for development purposes, but you may not redistribute the mappings complete and unmodified. Microsoft makes no warranties, express or implied, with respect to the mappings provided here. Use and modification of source code for Minecraft: Java Edition is governed by the Minecraft End User License Agreement available at https://account.mojang.com/documents/minecraft_eula.
# (c) 2019 Microsoft Corporation. All rights reserved. This information is provided "as-is" and you bear the risk of using it. This information does not provide you with any legal rights to any intellectual property in any Microsoft product. You may copy and use this information for your internal, reference purposes. Microsoft makes no warranties, express or implied, with respect to the information provided here.
Per Dinnerbone, any obfuscation mapping released before the license update on 14th August 2020 would be still available under this older license in addition to being available under the new license.
|September 3, 2019||Dinnerbone mentions "a small surprise for modders!" for 19w36a.|
|1.15||19w36a||Downloads to client and server obfuscation maps are now included in client.json.|
|September 4, 2019||Dinnerbone releases obfuscation mappings for 1.14.4 as well.|
|August 12, 2020||Dinnerbone indicates the license of the obfuscation maps will be updated and encourages modders to switch to Mojang's obfuscation map, claiming in another tweet that it would "help with compatibility".|
|He offered a preview of the updated license as well.|
|August 14, 2020||The license of obfuscation maps was updated.|
|The version_manifest.json was updated to have client.json entries for 1.14.4 and versions since 19w36a to link to updated obfuscation maps.|
|1.17||21w03a||Altered the wording of the license.|
- Out of all Java Edition versions published after 19w36a (September 4, 2019), Combat Test 3 is yet the only one published without any obfuscation map.
- Before the August 16th, 2020 license update, versions released in year 2020 had
# (c) 2019 Microsoft Corporation.in the license notice in the obfuscation map files.
- Despite that Combat Test 8b is published after the license update, it still uses the old license notice and has the 2019 year notice.
- In client obfuscation mappings, the very first function listed is called
youJustLostTheGame(), an easter egg reference to The Game.
- This function is used to trigger a Java crash after holding the debug key combination Ctrl + F3 + C for ten seconds.
- "ProGuard manual | Usage" – Guardsquare.
- "I've been pushing for this for a while, so I'm really happy that we were finally able to release the obfuscation mappings public. @SeargeDP had a great idea to release the 1.14.4 mappings as comparison, so those are going out right now." – @Dinnerbone on Twitter, September 4, 2019
- "ProGuard manual | Retrace" – Guardsquare.
- "Tomorrow's snapshot has a small surprise for modders! Should make one or two people happy :)" – @Dinnerbone on Twitter, September 3, 2019
- "Happy modding!" – @adrian_ivl on Twitter, September 4, 2019
- "This should answer the questions of everyone who kept asking about MCP updates for newer versions of Minecraft. Spoiler: there won't be any, they are finally not necessary anymore." – @SeargeDP on Twitter, September 4, 2019
- "We would like to see projects start to switch to the official Mojang names, to help bring the entire modding community together and help with compatibility." – @Dinnerbone on Twitter, August 12, 2020
- "Existing mappings will still be available under the old terms, but we will also republish them with the new terms on Friday. All new mappings provided in the future will be under the new terms." – @Dinnerbone on Twitter, August 12, 2020