Launcher problems

java.lang.ClassNotFoundException: net.minecraft.client.Minecraft

What the log looks like

java\.lang\.ClassNotFoundException:\s*net\.minecraft\.client\.Minecraft\b
Failed to find/access Minecraft main class:\s*java\.lang\.ClassNotFoundException:\s*net\.minecraft\.client\.Minecraft\b

How to fix it

  1. Make sure you are connected to the internet and launch the instance in Online Mode at least once so your launcher can download the missing base Minecraft jar and libraries.
  2. In Prism Launcher or MultiMC, right-click the broken instance, select Edit -> Version, highlight Minecraft in the component list, and click Revert (or re-select the version) to repair corrupted launch metadata.
  3. Move your launcher or instance folder if any parent folder name contains an exclamation mark (!) or unusual symbols, as Java's URLClassLoader cannot read jar files inside paths containing '!'.
  4. If you linked or imported an external modpack folder (such as from an old FTB launcher), back up your saves and config folders and recreate the instance cleanly using your launcher's built-in modpack import tool.
LoadersVanilla, Forge, Fabric
SeverityStops the game
CategoryLauncher problems

Check your own log

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