- A launcher is the program that signs you in, picks a version, and starts the game.
- A client is the running game itself, including any mods loaded into it.
- The launcher runs before you play; the client runs while you play.
- Mods load inside the client. The launcher only picks the profile and starts it.
A launcher is the program that picks your version, signs you in, and starts Minecraft. A client is the actual game that runs once it starts, including any mods loaded into it. The launcher is the front door; the client is the room you walk into. You use both, and they do different jobs.
What a launcher does
A launcher is the small app you open before you play. It does the setup work and then hands off to the game.
A launcher usually handles:
- Sign-in with your Microsoft account.
- Choosing a Minecraft version to run.
- Downloading the game files and Java for that version.
- Picking a profile or installation, including one set up for a mod loader.
- Setting memory and other launch options, then starting the game.
When you press play, the launcher builds the command that starts the game and then steps out of the way. It is not running while you play.
What a client does
A client is the game itself: the running instance of Minecraft you see and control. "Vanilla client" means the unmodified game. A modded client is the same game with mods loaded into it through a mod loader like Fabric.
So when people talk about a "utility client" or a "custom client," they mean a modified version of the running game, not a separate launcher. The mods add features once the game is already up.
How they fit together
The launcher starts the client. That is the whole relationship.
Open the launcher and sign in
You open the launcher and sign in with your account.
Pick a version or profile
You pick a version or a modded profile to run.
Launch the game
The launcher downloads what it needs and starts the game.
The client runs
The client runs. If you chose a mod loader profile, your mods load now.
A mod loader sits between the two. You install Fabric for your version, which adds a launch profile. The launcher then starts the game through that profile, and the loader pulls your mods in as the client boots. The launcher does not know or care which mods you have; it just starts the version you chose.
Where Opal fits
Opal is a Fabric mod, so you do not need a special launcher to run it. Set up a Fabric profile in your usual launcher, then add Opal like any other mod. See the setup guide to get going, or the scripting intro once it is loaded.
Launcher vs client at a glance
| Launcher | Client | |
|---|---|---|
| What it is | App that starts the game | The running game itself |
| When it runs | Before you play | While you play |
| Job | Sign in, pick version, launch | Render the world, run mods |
| Mods | Picks a modded profile | Actually loads and runs the mods |
| Example | The official Minecraft launcher | Vanilla or a modded game |
Do third-party launchers replace the client?
Some launchers do more than the official one. They manage modpacks, swap between many versions, or bundle a mod loader so you can skip the manual setup. A few popular clients ship their own launcher as well.
Even then, the split holds: the launcher's job is still to start the game, and the client is still what runs. A launcher that installs mods for you is just doing the setup step ahead of time. The mods themselves only matter once the client is running.
FAQ
No. A launcher is the program that signs you in and starts the game. A client is the game that runs after launch, including any mods. You use a launcher to start a client.
Not always. The official launcher can run a mod loader profile once Fabric or another loader is installed. Some third-party launchers bundle the loader to make setup easier, but they are still just starting the game.
The client. The launcher picks a modded profile, but the mod loader loads your mods as the game boots, so the mods run inside the client.
No. A custom or utility client is a modified game, loaded through a mod loader. It runs after the launcher starts the game.
