OpenCode Minecraft

A Fabric mod that integrates OpenCode into Minecraft Java Edition single player, with a unique pause mechanic that freezes the game while the AI is waiting for input and resumes when it's actively working.

Demo

MinecraffCodeLowRes_under10mb.mp4

Features

• Smart Pause Mechanic - Game automatically pauses when the AI is idle, letting you focus on coding without your character dying. Resumes instantly when the AI starts working.
• In-Game Chat Interface - Send prompts and receive responses directly in Minecraft chat using /oc commands.
• Session Management - Create, list, and switch between coding sessions without leaving the game.
• Real-Time Streaming - See AI responses as they're generated, token by token.
• Tool Visibility - Get feedback about what tools the AI is using (reading files, writing code, etc.).
• Configurable - Set your working directory, server URL, and other options.
• Cross-Platform - Works on macOS, Windows, and Linux.

Quick Start

1. Install Fabric Loader and Fabric API for Minecraft 1.21.4
2. Download the mod JAR from Releases and place it in your .minecraft/mods folder
3. Start OpenCode server: opencode serve
4. Launch Minecraft and create/join a single player world
5. Use /oc session list & /oc session join #
6. Start coding with /oc <your prompt here>

Requirements

• Minecraft 1.21.4
• Fabric Loader 0.16.10+
• Fabric API
• Java 21+
• OpenCode running in server mode (opencode serve)

Installation

Option 1: Download Release (Recommended)

1. Install Fabric API (required dependency)
2. Download the latest opencode-minecraft-x.x.x.jar from Releases
3. Place both JAR files in your .minecraft/mods folder

Option 2: Build from Source

git clone https://github.com/anthropics/opencode-minecraft.git
cd opencode-minecraft
./gradlew build

The built JAR will be in build/libs/opencode-minecraft-1.0.0.jar

Note: You still need to install Fabric API separately.

Commands

Command	Description
/oc <prompt>	Send a prompt to OpenCode
/oc status	Show connection and session status
/oc session new	Create a new coding session
/oc session list	List available sessions (numbered)
/oc session use <#>	Switch to session by number or ID
/oc cancel	Cancel current generation
/oc pause	Toggle pause control on/off
/oc config url <url>	Set server URL
/oc config dir <path>	Set working directory
/oc help	Show help

How the Pause Mechanic Works

The mod uses Minecraft's integrated server to control game simulation:

AI State	Game State	What's Happening
Idle	Paused	AI is waiting for your next prompt
Busy	Running	AI is processing (reading files, planning, etc.)
Generating	Running	AI is actively outputting text
Disconnected	Paused	Not connected to OpenCode server

When paused:

• World simulation stops (mobs freeze, time stops)
• You cannot move or interact
• A dark overlay shows the current status
• Chat remains functional for commands

A 3-second grace period after joining a world prevents immediate pausing.

Configuration

Configuration is stored in .minecraft/config/opencode.json:

{
  "serverUrl": "http://localhost:4096",
  "workingDirectory": "/path/to/your/project",
  "lastSessionId": null,
  "autoReconnect": true,
  "reconnectIntervalMs": 5000,
  "showStatusBar": true
}

Option	Default	Description
serverUrl	http://localhost:4096	OpenCode server URL
workingDirectory	User home	Project directory for file operations
lastSessionId	null	Auto-resume last session on connect
autoReconnect	true	Automatically reconnect if disconnected
reconnectIntervalMs	5000	Reconnection attempt interval
showStatusBar	true	Show status in action bar

Troubleshooting

"Not connected to OpenCode server"

• Ensure OpenCode is running: opencode serve
• Check if the server is accessible at http://localhost:4096
• Verify serverUrl in config matches your server

Game stays paused

• Use /oc status to check the current state
• If stuck, use /oc pause to toggle pause control off
• Ensure OpenCode server is running and responsive

No response in chat

• Create a session first: /oc session new
• Check /oc status for connection issues
• Look at Minecraft logs for errors

"Connection Lost" when joining world

• Ensure you're using the correct mod version for Minecraft 1.21.4
• Try ./gradlew clean build if building from source
• Check for conflicting mods

Development

# Build the mod
./gradlew build

# Run Minecraft with the mod (for development)
./gradlew runClient

See CONTRIBUTING.md for development guidelines.

How It Works (Technical)

The mod consists of several key components:

• OpenCodeClient - Coordinates HTTP communication and event handling
• SessionManager - Manages session lifecycle and state
• PauseController - Determines when to pause/resume based on AI state
• Mixins - Hook into Minecraft's integrated server to control ticks

Communication with OpenCode:

• REST API for session management (/session/* endpoints)
• Server-Sent Events (SSE) at /global/event for real-time updates
• Pause state is driven by session.status events (idle vs busy)

Contributing

Contributions are welcome! Please see CONTRIBUTING.md for:

• Development setup
• Code style guidelines
• How to submit pull requests
• Mixin best practices

License

MIT License - see LICENSE for details.

Related Projects

• OpenCode - The agentic coding tool this mod integrates with