When I was trying to use Forge1.12.1 I couldn’t launch it because the Minecraft Launcher wasn’t donwloading 1.12.1files complately in the first place.
This is the launch log
[Info: 2025-11-09 12:18:44.0824806: 3xK4YDD1asM=: NetQueue.cpp(100)] NetQueue: Action finished: https://s3.amazonaws.com/Minecraft.Download/indexes/legacy.json [Warning: 2025-11-09 12:18:44.0833935: 3xK4YDD1asM=: Downloadable.cpp(223)] Couldn't download %USERPROFILE%\AppData\Roaming\.minecraft\assets\indexes\legacy.json after (0) retries : FAILED_TO_DOWNLOAD Details: URL: https://s3.amazonaws.com/Minecraft.Download/indexes/legacy.json Name: legacy.json File: <WORKDIR>\.minecraft\assets\indexes\legacy.json [Info: 2025-11-09 12:18:44.0850858: 3xK4YDD1asM=: MinecraftJavaLoggingContext.cpp(65)] Launcher/launcher (main) Error Unable to download https://s3.amazonaws.com/Minecraft.Download/indexes/legacy.json to <WORKDIR>\.minecraft\assets\indexes\legacy.json [Warning: 2025-11-09 12:18:44.0851159: 3xK4YDD1asM=: NetQueue.cpp(122)] Action https://s3.amazonaws.com/Minecraft.Download/indexes/legacy.json failed in response handler. response code: 404 - error string: '
Environment
Windows11
Thank you for your report!
However, this issue is Invalid.
Your game, launcher or server is modified.
If you can reproduce the issue in a vanilla environment, please recreate the issue.
Any non-standard client/server/launcher build needs to be taken up with the appropriate team, not Mojang.
Any plugin issues need to be addressed to the creator of the plugin or resource pack.
If you have problems on large servers like Hypixel, please contact them first as they run modified server software.
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