Mod switcher automatically changes the mods in the mods folder when you launch the game.

A "mod profile" is a folder in .minecraft/mods/profiles that contains a set of mods that are to be used with a certain profile from the Minecraft launcher. When a mod profile is launched all mods currently in the mods folder will be moved back to their corresponding mod profile folder and all mods in the launched mod profile folder will be moved into the mods folder.

Mod switcher can optionally be configured by creating/editing the file modswitcher.json in the profiles folder.

When Minecraft is started the launcher profile name will be matched against a folder in the profiles directory. If there is no folder with the same name as the launcher profile the default profile will be launched instead.

When Minecraft is started the launcher profile name will be attempted to be matched against the regex keys of the profiles object starting from the top. If a match is found of the value of the pair is used as the profile to be launched. If no match is found the default profile is launched.

When the launcher profile Fabric 1.20.4 is started from the Minecraft launcher all the mods will be moved out of the mods folder and back to their mod profile folder and mods in the profiles/Fabric 1.20 folder will be moved to the mods folder. Note that the periods (.) are escaped with a backslash (\) because Fabric 1\.20.\.4 is a regex and in regex . matches any character, not just periods (.).

{
  profiles: {
    "Fabric 1\.20\.4": "Fabric 1.20",
    "Vanilla+": "VanillaPlus"
  }
}