Creating unityctl Plugins Skill

Creating unityctl Plugins

There are two plugin types: script (C# running inside Unity) and executable (any program on disk).

Script Plugins

Run C# inside the Unity Editor via the script.execute RPC. Best for commands that need Unity APIs.

Quick start

unityctl plugin create my-tool   # scaffolds .unityctl/plugins/my-tool/

Structure

.unityctl/plugins/my-tool/
  plugin.json    # manifest
  hello.cs       # handler script

plugin.json

{
  "name": "my-tool",
  "version": "1.0.0",
  "description": "My custom tool",
  "commands": [
    {
      "name": "stats",
      "description": "Show scene stats",
      "arguments": [
        { "name": "scene", "description": "Scene name", "required": false }
      ],
      "options": [
        { "name": "verbose", "type": "bool", "description": "Show details" },
        { "name": "format", "type": "string", "description": "Output format" }
      ],
      "handler": { "type": "script", "file": "stats.cs" }
    }
  ],
  "skill": { "file": "SKILL.md" }
}

Handler script

Must define public class Script with a static Main(string[] args) method — sync object, async Task<T>, or async Task. Arguments and options are passed as the args array.

using UnityEngine;
using UnityEditor;

public class Script
{
    public static object Main(string[] args)
    {
        var count = Object.FindObjectsByType<GameObject>(FindObjectsSortMode.None).Length;
        return $"Scene has {count} GameObjects";
    }
}

The return value is sent back as the command output. Task<T> returns are awaited and unwrapped before serialisation. The script runs on Unity's main thread and has access to all Unity and UnityEditor APIs. Add using System.Threading.Tasks; when writing an async handler.

Custom skill documentation

Add a "skill": { "file": "SKILL.md" } entry to plugin.json and create the markdown file. It will be included in the composed SKILL.md when running unityctl skill rebuild. Without it, documentation is auto-generated from the manifest.

Location

| Level | Directory | Precedence | |-------|-----------|------------| | Project | .unityctl/plugins/ | Higher | | User | ~/.unityctl/plugins/ | Lower |

Use --global / -g with plugin create to scaffold at user level.

Plugin names must be lowercase alphanumeric with hyphens (e.g. my-tool, scene-stats). Must start and end with a letter or digit.

Executable Plugins

Any executable named unityctl-<name> becomes available as unityctl <name>. Best for workflows outside Unity: build pipelines, CI scripts, multi-step orchestration.

How it works

Place an executable (shell script, Python, Go binary, .bat/.cmd/.ps1 on Windows) named unityctl-<name> in .unityctl/plugins/ or on PATH. All arguments after the command name are passed through.

Executables in plugin directories are registered at startup (appear in --help). Executables on PATH are resolved lazily when invoked — like git resolving git foo → git-foo.

unityctl smoke 30          # finds and runs unityctl-smoke with arg "30"
unityctl deploy --staging  # finds and runs unityctl-deploy with arg "--staging"

Environment variables

The CLI sets these before launching the executable:

| Variable | Description | |----------|-------------| | UNITYCTL_PROJECT_PATH | Resolved Unity project root | | UNITYCTL_BRIDGE_PORT | Bridge HTTP port | | UNITYCTL_BRIDGE_URL | Full bridge URL (e.g. http://localhost:62908) | | UNITYCTL_AGENT_ID | Agent ID if --agent-id was passed | | UNITYCTL_JSON | "1" if --json was passed |

Example

#!/usr/bin/env bash
# Save as: unityctl-smoke (chmod +x)
unityctl logs clear
unityctl play enter
sleep "${1:-10}"
unityctl screenshot capture --json > /tmp/smoke.json
ERRORS=$(unityctl logs -n 1000 --json | jq '[.entries[] | select(.level == "Error")] | length')
unityctl play exit
[ "$ERRORS" -eq 0 ] && echo "PASS" || { echo "FAIL: $ERRORS error(s)"; exit 1; }

Companion skill file

Place unityctl-<name>.skill.md next to the executable to provide custom documentation for SKILL.md composition. Without it, a minimal section is auto-generated.

Platform notes

Windows: matches .exe, .cmd, .bat, .ps1 extensions
Unix: matches any file with execute permission; extensions are stripped from the command name (unityctl-foo.sh becomes unityctl foo)

Precedence

built-in command > script plugin > executable plugin. A plugin cannot shadow a built-in command.

After changes

Run unityctl skill rebuild to update the composed SKILL.md with plugin documentation.

Management commands

unityctl plugin list              # list all plugins (script + executable)
unityctl plugin create <name>     # scaffold a script plugin
unityctl plugin create <name> -g  # scaffold at user level (~/.unityctl/plugins/)
unityctl plugin remove <name>     # remove a script plugin

Agent Skills: Creating unityctl Plugins

Install this agent skill to your local

Skill Files