Install the MCP mod + Fabric API (Step 2 of 4)

This is Phase 2 of the four-phase Minecraft Java MCP setup. It assumes Phase 1 (setup-fabric) is done: Fabric is installed and the mods/ folder exists. You should have, written down:

• the chosen Minecraft version (e.g. 26.3);
• the mods-folder path (single-player) or the <server> root with its mods/ folder (dedicated server).

If either is missing, get it before continuing. Work interactively — confirm each download before moving on.

What you're installing

The MCP server is delivered as a Fabric mod. It needs exactly two jars in mods/, both matching the same Minecraft version:

1. The MCP mod — minecraft-fabric-mcp-<modver>+<mc-version>.jar.
2. Fabric API — the mod's only dependency.

Match the Minecraft version on both jars. A jar built for 26.1.2 will not load on 1.21.11, and vice versa. The version suffix after the + must equal the version chosen in Phase 1.

Step 1 — Download the MCP mod jar

From the mod's releases: https://github.com/chapmanjw/minecraft-java-fabric-mcp-server/releases

Pick the asset whose filename ends in +<your-mc-version>.jar — e.g. minecraft-fabric-mcp-1.2.0+26.3.jar for Minecraft 26.3. Pin to a specific release tag rather than tracking latest, so the version stays in lockstep with Minecraft and Fabric API.

Step 2 — Download the matching Fabric API jar

From Modrinth: https://modrinth.com/mod/fabric-api/versions

Filter by your Minecraft version and download the Fabric API jar for it — e.g. fabric-api-0.165.0+26.3.jar. Its Minecraft version must match exactly. Each mod jar also requires Fabric API at or above its pin (0.141.6+1.21.11, 0.145.4+26.1.1, 0.155.3+26.1.2, 0.161.0+26.2, 0.165.0+26.3); an older Fabric API fails to load, so filtering by Minecraft version alone does not guarantee a new enough jar.

The mod jar declares an EXACT depends.minecraft, so a jar built for one Minecraft version is refused at load on any other — you get a clear loader error rather than a crash later. Do not mix versions across the two jars.

Step 3 — Put both jars in mods/

Copy both jars into the mods/ folder from Phase 1.

Single-player — the platform path:

Dedicated server — <server>/mods/:

mkdir -p /opt/fabric-mcp/mods
# copy both jars into it

The folder should now contain exactly these two jars (plus any other mods the user already runs):

mods/
├── fabric-api-0.165.0+26.3.jar
└── minecraft-fabric-mcp-1.2.0+26.3.jar

Confirm with the user that both files are present and that the version suffixes match each other and the Minecraft version.

Step 4 — Quick load check (optional but recommended)

If the user wants to confirm the mod loads before configuring it:

• Single-player: launch the Fabric profile and load any world.
• Dedicated server: java -Xmx2G -jar fabric-server-launch.jar nogui.

In the log, look for the mod's startup lines:

[minecraft_fabric_mcp] MCP server config loaded from .../config/minecraft_fabric_mcp/config.json
[minecraft_fabric_mcp] Registered N MCP tools (M skipped due to version/module constraints)
[minecraft_fabric_mcp] MCP server listening at http://127.0.0.1:8765 (...)

Seeing the listening line means the mod loaded and the embedded MCP server started. (Phase 3 covers configuring it and verifying /healthz.) If the game crashes on load, the usual cause is a version mismatch between the mod jar, the Fabric API jar, and Minecraft — re-check the +<version> suffixes.

Wrap up

Confirm with the user:

• MCP mod jar for the chosen Minecraft version is in mods/.
• Matching Fabric API jar is in mods/.
• Both version suffixes match each other and the Minecraft version.
• (Optional) The mod loaded and logged the MCP listening line.

Hand off: Phase 2 is done — the mod is installed. The next step configures the MCP server (config.json), launches it, and verifies it's reachable. Offer to continue with the setup-server skill now.