LLM Dev Tools

Unity Editor tooling for AI-assisted development. AgentBridge exposes a file-based command protocol so external tools (Claude Code, scripts, CI) can drive the Unity Editor — and MCP turns every command into a tool your LLM can call directly.

Quickstart

1. Install the package

Window → Package Manager → + → Add package from git URL

https://github.com/simonwittber/AgentBridge.git

Or for a specific version:

https://github.com/simonwittber/AgentBridge.git#v0.1.0

2. Build the CLI

Download a pre-built binary from the latest release and place it on your PATH. Or build from source:

cd path/to/AgentBridge/Harness~/dffrnt-agent
go build -o dffrnt-agent .        # macOS / Linux
go build -o dffrnt-agent.exe .    # Windows

3. Wire into Claude Code

Add to .claude/settings.json inside your Unity project:

{
  "mcpServers": {
    "unity": {
      "command": "dffrnt-agent",
      "args": ["serve"]
    }
  }
}

Run dffrnt-agent from your Unity project root, or pass --project <path> to point it at the project directory.

4. Open Unity and verify

Start (or focus) your Unity project. In Claude Code, the unity MCP server will appear in /mcp with all bridge commands available as tools.

5. Send your first command

dffrnt-agent status

Expected output:

{
  "cmd": "status",
  "status": "ok",
  "uptime_s": 42.3,
  "queued": 0,
  "busy": false
}

Related MCP server: MCP For Unity

Requirements

• Unity 6000.0 or later

• Go 1.25+ (only needed to build from source)

Built-in commands

Core

Scene

Hierarchy & objects

Components & assets

Editor & console

Adding custom commands

Implement IAgentCommand in any Editor assembly:

using System.Text.Json.Nodes;
using LLMDevTools;
using UnityEditor;

[InitializeOnLoad]
public class MyCommand : IAgentCommand
{
    static MyCommand() => AgentBridge.Register(new MyCommand());

    public string    Cmd         => "my_cmd";
    public string    Description => "Does something useful.";
    public ArgSpec[] Args        => new[]
    {
        new ArgSpec("message", "string", "", "Text to log"),
    };

    public JsonObject Execute(string uid, string requestJson)
    {
        var resp = AgentBridge.MakeResponse(uid, Cmd, "ok");
        resp["echoed"] = requestJson;
        return resp;
    }
}

Protocol

Commands are newline-delimited JSON written to Temp/agent_input:

{"uid":"a1b2c3d4","cmd":"compile"}

Responses are appended to Temp/agent_output:

{"uid":"a1b2c3d4","cmd":"compile","status":"ok","session_id":1749123456789,"errors":[],"warnings":[]}

Unity also writes Temp/agent_session every 5 seconds:

{"pid":12345,"state":"idle","active_scene":"Main","play_mode":false,"compile_errors":0,"written_at":1749123456789}

dffrnt-agent reads this file to verify Unity is alive before sending any command. Output rotates at 2 MB; input is truncated on Unity startup.

Testing

Unit tests (Go)

cd Harness~/dffrnt-agent
go test ./...

End-to-end tests (MCP → Unity)

These tests spawn the installed dffrnt-agent binary (must be on PATH) and drive it over the MCP protocol against a live Unity session. Build and install the binary first, open the Example~ project in Unity, then:

cd Harness~/dffrnt-agent
UNITY_PROJECT=/path/to/AgentBridge/Example~ go test -v -run TestMCP -timeout 300s

On Windows (PowerShell):

$env:UNITY_PROJECT = "C:\path\to\AgentBridge\Example~"
go test -v -run TestMCP -timeout 300s

If UNITY_PROJECT is not set, the tests default to ../../Example~ relative to the test directory. Tests are automatically skipped if Unity is not running or the session file is missing or stale.

Note: TestMCP_Refresh triggers a full AssetDatabase.Refresh() which can take 2+ minutes on a fresh project. Subsequent runs are much faster.

LLM Agent Log window

Open via Window → General → LLM Agent Log. Live scrolling view of all commands and responses — green = ok, red = error.