Game Designer

Game Designer

Convert a one-line natural-language game description into a strictly-schemaed GDD JSON. The output is consumed unchanged by every downstream stage — be concrete, internally consistent, and machine-readable.

When to use

The orchestrator (gameforge) invokes this skill once per project, immediately after init. The host agent provides:

• The user's description (1-3 sentences)
• Optional: preferred genre hint

Output contract

Output ONLY a single JSON object matching this schema. No prose, no fences, no commentary.

{
  "title": "<short game title (1-4 words)>",
  "genre": "top-down-adventure" | "platformer" | "action-platformer" | "twin-stick-shooter" | "puzzle" | "shoot-em-up" | "dungeon-crawler" | "top-down-rpg" | "beat-em-up",
  "tagline": "<one-sentence pitch>",
  "loop":   "<1-3 sentences describing the core gameplay loop>",
  "winCondition":  "<concrete, observable in headless test, e.g. 'window.__gameState.gemsCollected >= 3'>",
  "loseCondition": "<concrete, e.g. 'window.__gameState.playerHp <= 0', or 'none' for endless>",
  "controls": {
    "movement": "8-direction" | "4-direction" | "platformer" | "twin-stick",
    "actions":  [{ "key": "<KEY>", "name": "<verb>", "description": "<what it does>" }]
  },
  "entities": [
    {
      "id":     "<SCREAMING_SNAKE_CASE>",
      "kind":   "player" | "enemy" | "npc" | "pickup" | "projectile" | "boss",
      "color":  "<short color phrase, e.g. 'muted purple-green'>",
      "desc":   "<vivid 1-line visual description>",
      "states": ["idle", "walk", ...],
      "speed":  <pixels/sec>,
      "hp":     <hit points (0 = invuln/static, 1 = one-shot)>
    }
  ],
  // NPC entities MAY include a personality block — used by gen_npc_dialogue to produce
  // rich, character-consistent dialogue at build time via Claude Haiku:
  // {
  //   "id": "NPC_ELDER", "kind": "npc", ...,
  //   "personality": {
  //     "openness": 0.6, "conscientiousness": 0.9, "extraversion": 0.4,
  //     "agreeableness": 0.8, "neuroticism": 0.1,
  //     "backstory": "One sentence about who this NPC is and why they're in this town."
  //   }
  // }
  // Values are 0.0–1.0 (Big-5 dimensions). backstory is used directly in the prompt.
  // If omitted, gen_npc_dialogue uses a generic description derived from the entity desc field.

  "tilesetPalette": [
    { "id": "<SCREAMING_SNAKE_CASE>", "color": "<#hex>", "passable": <bool> }
  ],
  "levelHints": {
    "size":   [<tilesWide>, <tilesTall>],   // each between 8 and 40
    "count":  <number of levels, 1-3>,
    "themes": ["<theme per level>"]
  }
}

Hard constraints

• Exactly one entity with kind === "player".
• Total entities: 4-9 (sprite-sheet row limit). Combine variants if needed.
• Tileset palette: 3-6 entries. First entry SHOULD be the dominant passable floor.
• Every entity's states MUST include "idle". For kind ∈ {player, enemy, boss}, also include "walk".
• Prefer states from this filter-safe set: idle, walk, jump, cast, block, victory. Avoid hurt and attack as dedicated sprite states — GPT Image 2's content filter trips on the typical "pained grimace / lunging / weapon extended" descriptions. For damage feedback, the codesmith uses tint flash + alpha blink + camera shake (no sprite frame needed). For attack feedback, a brief swing animation can be implemented in code.
• winCondition and loseCondition must be testable from window.__gameState without human judgment.
• For platformer / action-platformer: include gravity-friendly tiles (floor, wall) and a goal entity OR goal tile.
• For beat-em-up: floor is always passable, walls are impassable on the sides only. No ceiling. Include ENEMY entity (kind=enemy) that walks toward player. Win = defeat N enemies.
• For top-down: orthogonal layout, walls block movement.
• Do not include music, audio, voice, or dialogue.

Genre-specific guidance

beat-em-up

Classic side-scrolling brawler (Double Dragon / Final Fight style). Characters move in both X and Y within a 2D "lane" depth illusion. Y-position determines render depth and ground-truth position on the pseudo-3D floor.

• Controls: 4-direction movement (X+Y pseudo-3D), attack on SPACE/Z
• Tiles: GROUND (passable), WALL (impassable left/right border), optional PROP tiles (bench, barrel)
• Camera follows player rightward only (one-way scroll)
• HUD: health bar drawn as graphics, score, lives/wave count
• winCondition: defeat a fixed number of enemies (e.g. window.__gameState.enemiesDefeated >= 10)
• Use the beat-em-up skill for codesmith patterns

action-platformer

Gravity-driven side-scroller with jump, hazards, and atmospheric depth (Shovel Knight / Metroidvania style).

• Controls: left/right + jump (SPACE), optional attack (Z)
• Tiles: STONE/BRICK (impassable floor/wall), SKY (passable, transparent — bg shows through), optional HAZARD tile (spikes)
• Camera follows player in both axes; world taller than viewport
• HUD: HP bar, score, level name
• Use bg-artist for cave/dungeon parallax background
• winCondition: reach goal tile OR collect all keys

Process

1. Read the user's prompt and any genre hint from the orchestrator.
2. Decide the genre (default to top-down-adventure for ambiguous prompts).
3. Pick a 1-4 word title that fits.
4. Choose the smallest entity set that captures the prompt (don't over-design — most jams need 4-5 entities).
5. Choose a tile palette that supports the genre (platformer needs solid floor + sky; top-down needs floor + walls + scenery).
6. Write win/lose conditions referencing window.__gameState fields the codesmith will populate (e.g. gemsCollected, coinsCollected, asteroidsDestroyed, playerHp).
7. Run scripts/validate_gdd.mjs <gdd-file> to confirm shape before returning.
8. Save to game-state.json under gdd.

Validation rules (encoded in scripts/validate_gdd.mjs)

• title and genre are non-empty strings.
• entities is a non-empty array; exactly one with kind === "player".
• Every entity id matches /^[A-Z][A-Z0-9_]*$/.
• Every entity's states includes "idle".
• tilesetPalette.length >= 2.
• levelHints.size is [w, h] with 16 <= w,h <= 40.

Examples

Prompt: "A pixel knight collects gems while dodging slimes."

GDD (excerpt):

{
  "title": "Slime Slayer",
  "genre": "top-down-adventure",
  "winCondition": "window.__gameState.gemsCollected >= 3",
  "entities": [
    { "id": "KNIGHT", "kind": "player", "color": "blue", "desc": "Small blue knight with a silver sword", "states": ["idle","walk","attack","hurt"], "speed": 80, "hp": 3 },
    { "id": "SLIME",  "kind": "enemy",  "color": "green", "desc": "Round green slime that wobbles", "states": ["idle","walk","hurt"], "speed": 30, "hp": 1 },
    { "id": "GEM",    "kind": "pickup", "color": "yellow","desc": "Bright sparkling gem", "states": ["idle"], "speed": 0, "hp": 0 }
  ]
}

See references/examples.md for a full GDD per genre.

Scripts

• scripts/validate_gdd.mjs <gdd-json-file> — fails non-zero with reason if invalid.

References

• references/gdd-schema.json — JSON Schema (draft-07).
• references/examples.md — one full GDD per supported genre.