Install Minecraft Java + Fabric (Step 1 of 4)

You are guiding the user through the first of four setup phases. Work interactively: do one thing, confirm it worked, then move on. Do not dump the whole procedure at once.

The big picture — explain this first

The user is building a stack that lets Claude read and change a live Minecraft Java Edition world. Unlike a separate server process, the MCP server is a Fabric mod that runs inside Minecraft itself. There are four setup phases, one per skill, run in order:

Tell the user this is Phase 1, and that each phase ends by handing off to the next. Budget ~10 minutes for a single-player setup, ~20–30 for a dedicated server.

Pin your versions — say this out loud. The mod ships a separate jar per Minecraft version, built against that version's Fabric API. A Minecraft or Fabric update can break the modding surface the mod depends on. Pick a supported Minecraft version, pin it, disable auto-update for that profile, and upgrade Minecraft, the Fabric API jar, and the mod jar together.

Gather context

Ask the user, before downloading anything:

1. Single-player or dedicated server?
   • Single-player (recommended default): Claude edits the world you play in, on your own machine. Loopback only, no token, no firewall changes. ~10 minutes.
   • Dedicated server: a headless Minecraft server (for friends, or to keep the MCP endpoint up 24/7). LAN/remote access with a bearer token. Branch the rest of this skill on their answer.
2. Which Minecraft version? The mod supports 1.21.11, 26.1.1, 26.1.2, 26.2, and 26.3. Default to the newest the user is comfortable with (26.3). Record the exact version — it must match the mod jar and Fabric API jar in Phase 2. The mod jar declares an EXACT Minecraft dependency, so a mismatch is refused at load with a clear message rather than failing later.
3. (Dedicated server only) What OS and where? Linux or Windows; same machine as Claude, LAN box, or cloud VM. The host needs a JDK: Java 21 for 1.21.11, Java 25 for every 26.x. (Single-player uses the launcher's bundled runtime — no separate JDK needed.) The connect step (Phase 4) cares where it runs, so note their answer.

Single-player branch

Step 1 — Install the Fabric loader

Send the user to the official installer: https://fabricmc.net/use/installer/

• Windows: download and double-click the .exe.
• macOS / Linux: java -jar fabric-installer-*.jar.

In the installer, pick the Client tab, select the Minecraft version chosen above, leave the default install location, and click Install.

Step 2 — Create the profile and the mods folder

Open the Minecraft Launcher. A new Fabric Loader profile should appear. Launch it once and then exit the game — this first run creates the .minecraft/mods/ folder Phase 2 drops jars into. The mods folder lives at:

Confirm with the user that the Fabric profile launched and the mods/ folder now exists. Record the mods-folder path — Phase 2 needs it.

Dedicated server branch

Step 1 — Install the Fabric dedicated server

Download the Server installer from https://fabricmc.net/use/server/ into a dedicated directory, then run it (substitute the chosen Minecraft version):

mkdir -p /opt/fabric-mcp
cd /opt/fabric-mcp
java -jar fabric-server-installer-*.jar server -mcversion 26.1.2 -downloadMinecraft

This produces fabric-server-launch.jar and downloads the Minecraft server jar. On Windows, use a stable path with no spaces (e.g. C:\fabric-mcp); avoid Program Files and OneDrive-synced folders. Use this folder as <server> for the rest of setup and record its absolute path.

Step 2 — First run + EULA

Run it once to generate server.properties and eula.txt, then stop it (Ctrl+C):

java -Xmx2G -jar fabric-server-launch.jar nogui

Open eula.txt and change eula=false to eula=true.

Step 3 — Confirm command access

For Claude's command-backed tools to work, the server must allow operator commands. In server.properties, confirm sensible defaults (e.g. gamemode=creative so agents can build freely if that suits the user). The MCP mod runs tool calls as the console, which has full command permission — no per-player op is required for the MCP tools themselves.

On 26.3 a dedicated server defaults to white-list=true, so the user's own character cannot join until added. Set white-list=false in server.properties for a private server, or run whitelist add <name> via command_execute. The MCP console tools are unaffected.

Wrap up

Confirm with the user (the relevant set for their branch):

• Minecraft version chosen and recorded; auto-update not relied on.
• Single-player: Fabric Loader profile created; launched once; mods/ folder exists and its path is recorded.
• Dedicated server: Fabric server installed; ran once; eula=true; server root path recorded; correct JDK present (21 for 1.21.11, 25 for every 26.x).

Then hand off: tell the user Phase 1 is done and the next step installs the MCP mod and its Fabric API dependency. Offer to continue with the setup-mod skill now.