AI Game Builder — Developer Guide

This skill is for developing the builder itself, not for generating games. Use it when modifying skills, the MCP server, the Godot editor plugin, hooks, or docs.

Architecture Overview

User prompt → Claude Code + plugin (skills + MCP + hooks)
                    │                           │
              Writes .gd/.tscn             MCP Server (Node.js)
              directly to disk                  │
                    │                    HTTP on port 6100
                    │                           │
              Godot auto-reloads      Godot Editor Plugin (GDScript)
                                      (bridge + dock + errors + scanner)

Three layers:

1. •Claude Code Plugin — Skills (SKILL.md files), hooks, .mcp.json, .claude-plugin/
2. •MCP Server — Node.js process (mcp-server/) bridging Claude ↔ Godot via stdio (MCP protocol) + HTTP (to Godot)
3. •Godot Editor Plugin — GDScript (godot-plugin/) running inside the Godot editor, HTTP server on port 6100

Claude Code starts the MCP server automatically via .mcp.json. The MCP server talks to the Godot editor plugin over HTTP. Users don't start anything manually except enabling the Godot plugin.

File Map

godot-ai-builder/
├── .claude-plugin/
│   ├── plugin.json              # Plugin manifest (name, version, author, keywords)
│   └── marketplace.json         # Marketplace registry entry
│
├── skills/                      # 14 game-generation skills + this dev skill
│   ├── godot-builder/SKILL.md   # Master router — entry point for all game requests
│   ├── godot-director/SKILL.md  # 6-phase build protocol (PRD → Foundation → ... → QA)
│   ├── godot-init/SKILL.md      # Project bootstrapping, folder structure
│   ├── godot-gdscript/SKILL.md  # GDScript syntax and patterns reference
│   ├── godot-scene-arch/SKILL.md # Scene building (programmatic vs .tscn)
│   ├── godot-physics/SKILL.md   # Collision layers, physics bodies
│   ├── godot-player/SKILL.md    # Player controllers (top-down, platformer, twin-stick, etc.)
│   ├── godot-enemies/SKILL.md   # Enemy AI, spawn systems, boss patterns
│   ├── godot-ui/SKILL.md        # UI screens, HUD, menus, transitions
│   ├── godot-effects/SKILL.md   # Audio, particles, tweens, visual effects
│   ├── godot-assets/SKILL.md    # Visual quality system, shaders, procedural art
│   ├── godot-polish/SKILL.md    # Game feel — screen shake, dissolve, hit flash, juice
│   ├── godot-ops/SKILL.md       # MCP tool operations (run, stop, errors, reload)
│   ├── godot-templates/SKILL.md # Genre-specific file manifests
│   └── godot-dev/SKILL.md       # THIS FILE — builder development guide
│
├── hooks/
│   ├── hooks.json               # Hook registration (Stop hook only)
│   └── stop-guard.sh            # Prevents Claude from quitting mid-build
│
├── .mcp.json                    # MCP server config (auto-launched by Claude Code)
│
├── mcp-server/
│   ├── index.js                 # MCP server entry — Server + StdioServerTransport
│   ├── package.json             # Dependencies: @modelcontextprotocol/sdk, sharp
│   └── src/
│       ├── tools.js             # TOOL_DEFINITIONS array (21 tools) + handleToolCall dispatcher + handlers
│       ├── godot-bridge.js      # HTTP client → Godot editor (port 6100)
│       ├── scene-parser.js      # .tscn text format parser
│       └── asset-generator.js   # SVG/PNG sprite generator (layered gradients, shadows, glow)
│
├── godot-plugin/
│   └── addons/ai_game_builder/
│       ├── plugin.cfg           # Godot plugin metadata
│       ├── plugin.gd            # EditorPlugin — starts bridge + dock
│       ├── http_bridge.gd       # HTTP server (port 6100) — route handlers
│       ├── dock.gd              # Bottom dock panel — status + log display
│       ├── dock.tscn            # Dock scene file
│       ├── error_collector.gd   # Two-strategy error detection (script validation + log scan)
│       └── project_scanner.gd   # File discovery for /state endpoint
│
├── knowledge/                   # Reference docs (copied into user projects by setup.sh)
│   ├── godot4-reference.md      # GDScript syntax, nodes, signals
│   ├── scene-format.md          # .tscn format spec
│   ├── game-patterns.md         # Architecture templates per genre
│   └── asset-pipeline.md        # Asset creation and import
│
├── setup.sh                     # Installs Godot plugin + knowledge into a project
├── README.md                    # Public README
├── GETTING-STARTED.md           # Full user walkthrough (6 steps)
└── GETTING-STARTED.pdf          # PDF version (generated via pandoc + typst)

Key Conventions

Skill Format

Each skill is a directory under skills/ containing a single SKILL.md file. The file has YAML frontmatter (name, description) and markdown body. Skills are namespaced as /godot-ai-builder:godot-* when the plugin is loaded.

---
name: godot-skillname
description: |
  One-paragraph description of what this skill does.
  Include trigger phrases so Claude knows when to load it.
---

# Skill Title

Content: patterns, code examples, checklists, rules.

Skill content IS the instruction set. There's no separate config — the markdown text directly controls what Claude does when it loads the skill. Write it as if you're briefing a senior developer on exactly how to do the job.

Skill Routing

godot-builder is the master router. It reads the user's prompt and loads specialized skills based on intent. When adding a new skill:

1. •Create skills/godot-newskill/SKILL.md
2. •Add it to the routing table in godot-builder/SKILL.md (Section "Route to Skills")
3. •Add keywords to the "Keyword Routing" section
4. •Add it to the "Skill Directory" tables

MCP Server Architecture

• •Entry: mcp-server/index.js — creates an MCP Server, registers ListToolsRequestSchema and CallToolRequestSchema
• •Tools: src/tools.js — exports TOOL_DEFINITIONS (array of MCP schemas) and handleToolCall(name, args) dispatcher
• •Bridge: src/godot-bridge.js — HTTP client that calls the Godot editor on port 6100
• •Protocol: MCP SDK over stdio (Claude ↔ MCP server) + HTTP JSON (MCP server ↔ Godot plugin)
• •Environment: GODOT_BRIDGE_PORT (default 6100), GODOT_PROJECT_PATH (default .)

Godot Editor Plugin Architecture

• •plugin.gd is the EditorPlugin entry — creates the HTTP bridge and dock on _enter_tree()
• •http_bridge.gd runs a TCPServer on port 6100, routing requests:
  • •GET /status → editor state
  • •GET /errors → error_collector results
  • •POST /run → run scene in editor
  • •POST /stop → stop running scene
  • •POST /reload → rescan filesystem
  • •POST /log → send message to dock panel
  • •POST /phase → update phase state, emit phase_updated signal
  • •GET /phase → return current phase state
  • •GET /scene_tree?max_depth=N → live scene tree hierarchy
  • •GET /class_info?class_name=X&inherited=bool → ClassDB lookup
  • •POST /add_node → add node to edited scene
  • •POST /update_node → modify node properties
  • •POST /delete_node → remove node from scene
  • •GET /screenshot?viewport=2d|3d → editor viewport capture (base64 PNG)
  • •GET /open_scripts → list open scripts in script editor
• •dock.gd displays phase progress bar, control buttons (Run/Stop/Reload), error badges, filtered log, and quality gates checklist. Connected to bridge via signals bridge_log(msg) and phase_updated(data)
• •error_collector.gd uses two strategies: active script validation + Godot log scanning
• •project_scanner.gd walks the filesystem for /state responses

Hook System

Only one hook: the Stop guard.

• •hooks/hooks.json registers a Stop event hook running stop-guard.sh
• •The script checks for .claude/.build_in_progress file
• •If present: blocks Claude from stopping (returns {"decision": "block", ...})
• •If absent: allows normal exit
• •The Director creates the file at Phase 0, removes it at Phase 6

Common Development Tasks

Adding a New MCP Tool

1. •Define the schema in mcp-server/src/tools.js — add to TOOL_DEFINITIONS array:

{
  name: "godot_new_tool",
  description: "What this tool does — be specific so Claude knows when to use it.",
  inputSchema: {
    type: "object",
    properties: {
      param_name: { type: "string", description: "..." },
    },
    required: ["param_name"],
  },
},

1. •Add dispatcher case in handleToolCall():

case "godot_new_tool":
  return await toolNewTool(args.param_name);

1. •Write the handler function:

async function toolNewTool(paramName) {
  await bridge.sendLog(`[MCP] Doing something with ${paramName}...`);
  // Implementation...
  const result = { /* response data */ };
  await bridge.sendLog(`[MCP] Done: ${paramName}`);
  return result;
}

1. •If the tool needs a new Godot endpoint, add a route in http_bridge.gd:

# In _route_request():
"/new_endpoint":
    _handle_new_endpoint(client, body)

And add the corresponding bridge function in godot-bridge.js:

export async function newEndpoint(data) {
  return bridgeRequest("POST", "/new_endpoint", data);
}

1. •

   Add logging — every tool handler should call bridge.sendLog() before and after.

2. •

   Document it — add the tool to:

   • •skills/godot-builder/SKILL.md (MCP tools list)
   • •skills/godot-ops/SKILL.md (operations reference)
   • •README.md (MCP Tools table)

Adding a New Skill

1. •Create skills/godot-newname/SKILL.md with YAML frontmatter
2. •Write the skill content (patterns, code examples, rules, checklists)
3. •Register in godot-builder/SKILL.md:
   • •Add to "Route to Skills" table
   • •Add keywords to "Keyword Routing"
   • •Add to "Skill Directory" tables
4. •If the Director should invoke it during builds, update godot-director/SKILL.md phase descriptions
5. •Update the README skill count and table

Modifying the Godot Editor Plugin

Files live in godot-plugin/addons/ai_game_builder/. Changes here require:

1. •Edit the files in the plugin source
2. •Run setup.sh again on any test project to copy updated files
3. •Restart Godot or disable/re-enable the plugin to pick up changes

Key GDScript patterns in the plugin:

• •All files are @tool scripts (run in editor, not game)
• •http_bridge.gd uses TCPServer + StreamPeerTCP for HTTP
• •Signals: bridge.log_message.emit(msg) → dock picks it up
• •error_collector.gd caches results, refreshed on /errors request
• •The plugin.gd stores editor_interface reference for editor API access

Modifying the Asset Generator

mcp-server/src/asset-generator.js exports:

• •generatePlaceholder(args) → SVG string + writes file
• •generatePng(args) → uses sharp to convert SVG → PNG

Entity type builders (each returns an SVG inner content string): buildCharacter, buildEnemy, buildBoss, buildProjectile, buildTile, buildIcon, buildBackground, buildNpc, buildItem, buildPickup, buildUi

Helpers: hexToRgb(), darken(), lighten(), withAlpha(), uid(), simplePrng()

When adding a new entity type:

1. •Add to DEFAULT_COLORS map
2. •Create a buildNewType(w, h, color, style) function
3. •Add the type string to the switch in the buildEntity() router
4. •Add the type to TOOL_DEFINITIONS enum in tools.js
5. •Test: call godot_generate_asset with the new type

Visual quality rules for SVGs:

• •Always use <radialGradient> or <linearGradient> — never flat fills
• •Include <filter id="shadow"> with <feDropShadow>
• •Layer: shadow → body → core/details → highlights → outline
• •Use darken(color) for shadows, lighten(color) for highlights
• •Every entity gets a glow/outline layer using gaussian blur filter

Updating Documentation

Files to update (keep them in sync):

• •README.md — public-facing, architecture diagram, install steps, skill table, tool table
• •GETTING-STARTED.md — user walkthrough (6 steps), troubleshooting, project structure
• •GETTING-STARTED.pdf — regenerate after editing the markdown

Regenerating the PDF:

cd /path/to/godot-ai-builder
pandoc GETTING-STARTED.md -o GETTING-STARTED.pdf --pdf-engine=typst

GitHub URL: https://github.com/HubDev-AI/godot-ai-builder Always use this URL in all docs and scripts. Check setup.sh too — it has inline URLs.

Adding a New Hook

1. •Add the hook definition to hooks/hooks.json:

{
  "hooks": {
    "EventName": [
      {
        "hooks": [
          {
            "type": "command",
            "command": "bash \"${CLAUDE_PLUGIN_ROOT}/hooks/new-hook.sh\"",
            "timeout": 10
          }
        ]
      }
    ]
  }
}

1. •

   Create the shell script in hooks/. It receives JSON on stdin and can return JSON to influence behavior.

2. •

   Available hook events: Stop, PreToolUse, PostToolUse, Notification

Modifying the Director Protocol

The Director (skills/godot-director/SKILL.md) controls the 6-phase build:

• •Phase 0: PRD (game design doc, visual tier choice)
• •Phase 1: Foundation (player, camera, background)
• •Phase 2: Abilities (shooting, jumping, interactions)
• •Phase 3: Enemies (AI, spawning, combat, scoring)
• •Phase 4: UI (menus, HUD, game over, transitions)
• •Phase 5: Polish (shaders, particles, screen shake, styled UI)
• •Phase 6: QA (error check, edge cases, final verify)

Each phase has quality gates — conditions that must pass before moving on. To modify a phase: edit the phase section in the Director skill and update its gates.

The Director also manages:

• •.claude/.build_in_progress file (build lock)
• •Visual tier selection (procedural/custom/AI-art/prototype)
• •Sub-agent delegation for parallel file writing
• •PRD template and approval flow

Checkpoint System

Structured build state saved to .claude/build_state.json after each phase completion.

MCP Tools:

• •godot_save_build_state — writes JSON checkpoint (direct filesystem, no bridge)
• •godot_get_build_state — reads JSON checkpoint, handles missing file gracefully
• •godot_update_phase — sends phase progress to Godot dock via bridge POST /phase

Data Model (.claude/build_state.json):

{
  "version": "1.0",
  "build_id": "unique-id",
  "timestamp": "ISO-8601",
  "game_name": "...",
  "genre": "...",
  "visual_tier": "procedural",
  "current_phase": { "number": 0, "name": "...", "status": "...", "started_at": "..." },
  "completed_phases": [{ "number": 0, "name": "...", "completed_at": "...", "quality_gates": {} }],
  "files_written": ["scripts/player.gd"],
  "error_history": [{ "file": "...", "message": "...", "resolution": "...", "resolved": true }],
  "test_runs": [{ "phase": 0, "errors": 0, "success": true }],
  "prd_path": "docs/PRD.md",
  "next_steps": ["..."]
}

Resume Flow:

1. •Director calls godot_get_build_state() at session start
2. •If found: show summary, ask user to continue or start fresh
3. •If continue: validate files exist, re-run quality gates for completed phases, resume from current_phase
4. •If fresh: delete checkpoint and build lock
5. •After Phase 6: delete both .claude/build_state.json and .claude/.build_in_progress

Enhanced Dock

The dock (dock.gd + dock.tscn) provides:

• •Phase progress bar (0-6) with colored status labels (green=completed, yellow=in_progress)
• •Control buttons: Run (▶), Stop (■), Reload (↻) — call bridge handlers directly, no HTTP round-trip
• •Error badges: poll error_collector every 2s, show red/green error count + yellow warning count
• •Log filtering: All / Errors / Progress tabs — message type detected from content keywords
• •Quality gates checklist: dynamic CheckBox nodes populated from phase_updated signal data

Signal flow: Director → godot_update_phase tool → bridge POST /phase → http_bridge.phase_updated signal → dock._on_phase_updated()

Cross-Cutting Patterns

Visual Quality Pipeline

Skills enforce visual quality through documentation rules:

1. •godot-assets — defines the 4-tier visual system, shader library, entity drawing patterns
2. •godot-player — visual standard for player entities (layered _draw(), sprite fallback)
3. •godot-enemies — visual standard for enemy entities (type-specific shapes, hit flash)
4. •godot-effects — shader effects (hit flash, dissolve, glow), particles, trails
5. •godot-polish — game feel checklist, shader-based polish, styled UI, transitions
6. •asset-generator.js — SVG generation with gradients, shadows, highlights

All these must stay consistent. When you change visual patterns in one skill, check the others.

Skill Cross-References

Skills reference each other. Key dependencies:

• •godot-builder → routes to ALL skills
• •godot-director → invokes skills per phase (player in P1, enemies in P3, UI in P4, polish in P5)
• •godot-polish → references shaders from godot-assets, effects from godot-effects
• •godot-player / godot-enemies → reference visual patterns from godot-assets
• •godot-ops → documents all MCP tools that other skills call

Logging Convention (MANDATORY)

Every MCP tool logs to the Godot dock via bridge.sendLog():

• •Prefix with [MCP] for tool operations
• •Prefix with [Agent: name] for sub-agent work
• •Log BEFORE and AFTER operations
• •Include meaningful details: file names, error counts, phase numbers
• •Logging is best-effort (silent failure) — never let a log failure break a tool

Additionally, every tool response includes a _dock_reminder field that reminds the AI to call godot_log() after the tool completes. This ensures the AI keeps the Godot dock updated constantly. The godot_log and godot_update_phase tool descriptions are marked ⚠️ MANDATORY to further reinforce this requirement.

Error Enforcement (HARD GATES)

The MCP server enforces error checking at the tool level — the AI cannot bypass these:

1. •

   index.js: Every tool response (except lightweight tools) includes _error_count from a live bridge check. If > 0, _action_required tells the AI to stop and fix.

2. •

   toolReloadFilesystem: After reloading, automatically calls bridge.getErrors() and includes _error_count and _error_files in the response. Logs a warning to the dock if errors exist.

3. •

   toolUpdatePhase with status="completed": Calls bridge.getErrors() first. If any errors exist, the completion is REJECTED — returns {ok: false, rejected: true} with error details. The phase is kept at "in_progress". This is the hardest gate: the AI literally cannot mark a phase complete while errors exist.

4. •

   getErrorCount(): Exported helper used by index.js to get a quick error count from the bridge's cached validation. Does NOT run headless Godot (that would be too slow for every call).

These gates ensure that even if the AI ignores skill instructions about error checking, the tools themselves force compliance.

Error Handling in MCP Tools

• •Bridge requests have a 5-second timeout
• •isConnected() checks by calling getStatus() — swallows errors
• •sendLog() wraps in try/catch — never throws
• •Tool handlers should throw descriptive errors — index.js catches and returns isError: true
• •project.godot parser is lenient — returns {} on missing file

Testing During Development

Testing MCP Tools

# Install dependencies
cd mcp-server && npm install

# Test the server starts
echo '{"jsonrpc":"2.0","id":1,"method":"tools/list"}' | node index.js

# Test with a running Godot instance (plugin enabled)
# The MCP server needs GODOT_PROJECT_PATH set to a real project
GODOT_PROJECT_PATH=/path/to/test/project node index.js

Testing the Godot Plugin

1. •Copy files: ./setup.sh /path/to/test/project
2. •Open test project in Godot
3. •Enable plugin in Project Settings → Plugins
4. •Check bottom dock appears with green status
5. •Test HTTP endpoints: curl http://localhost:6100/status

Testing Skills

Skills are just markdown — test by loading the plugin and using the skill:

cd /path/to/test/project
claude --plugin-dir /path/to/godot-ai-builder
# Then: /godot-ai-builder:godot-skillname

Testing Asset Generation

# Quick test: generate assets and inspect the SVGs
cd /path/to/test/project
claude --plugin-dir /path/to/godot-ai-builder
# Then ask: "Generate a character sprite" or "Generate an enemy sprite"
# Check the output SVG in assets/sprites/

Pitfalls & Lessons Learned

Edit Tool Accuracy

When editing files, ALWAYS re-read the file first to get exact strings. Old strings from memory or previous sessions may not match the current file contents. Failed edits cascade — if one Edit fails in a parallel batch, siblings may fail too.

Skill Text is Everything

There is no runtime config for skills. The SKILL.md content IS the instruction set. If Claude doesn't do something, the skill text needs to be more explicit. If Claude does something wrong, the skill needs a rule against it.

SVG Quality Matters

Early SVGs were flat colored shapes (triangles, rectangles). Users found them ugly. The asset generator was rewritten with layered gradients, shadows, highlights, and entity-specific builders. When modifying SVGs, always maintain:

• •Gradient fills (radialGradient or linearGradient)
• •Drop shadow filter
• •At least 3 visual layers (shadow, body, highlight)
• •Glow/outline effects for important entities

Cross-Skill Consistency

All visual skills must agree on patterns. A change to how player visuals work (godot-player) must be reflected in the effects that apply to players (godot-effects, godot-polish). The visual checklist in godot-assets is the authoritative source.

The project.godot Fragility

Claude has a tendency to overwrite project.godot sections. The builder skill explicitly warns against this: "ALWAYS read before modifying, NEVER overwrite, MUST preserve [autoload]". If you see game-breaking bugs after builds, check if project.godot sections were stripped.

PDF Regeneration

After updating GETTING-STARTED.md, always regenerate the PDF:

pandoc GETTING-STARTED.md -o GETTING-STARTED.pdf --pdf-engine=typst

Both pandoc and typst must be installed. On macOS: brew install pandoc typst.

setup.sh URL

The setup.sh file contains inline URLs for marketplace instructions. Keep these in sync with the real GitHub URL (https://github.com/HubDev-AI/godot-ai-builder).

MCP Server Auto-Start

The MCP server is launched automatically by Claude Code via .mcp.json. Users don't need to start it manually. The config uses ${CLAUDE_PLUGIN_ROOT} to resolve paths relative to the plugin directory.

Error Collector Strategies

error_collector.gd uses two strategies:

1. •Active script validation — parses .gd files for syntax errors
2. •Log scanning — reads Godot's output log for runtime errors Both run on /errors request. The active strategy catches errors that Godot's log doesn't always surface (e.g., scripts that fail to parse).

Commit Convention

Follow the existing commit style:

type: short description

Longer explanation if needed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Types used: feat, fix, docs, refactor Recent examples:

• •feat: visual quality overhaul — layered procedural visuals, shaders, polished SVGs
• •fix: rewrite error collector to actively validate scripts
• •docs: update guides with scope choice, godot_log tool, and dock logging
• •feat: add godot_log MCP tool + dock console logging for all operations