Minecraft wiki entry for Client.jar, associated text: The client.jar file is found in its version folder. It is accompanied by the client.json file that lists the version's attributes. Normal versions are available to choose from via the launcher, and snapshots are also available. It is also possible to download old alpha versions and create version files to install mods on. Note that creating a new version is the only way to install mods; the launcher keeps normal versions synced.