Design

This skill writes system-level design and art documents after /gat-brainstorm has established the game overview, systems index, and global art direction. For story, worldbuilding, characters, quests, dialogue, or authored narrative content, delegate to /gat-story. For the initial concept interview, it delegates to /gat-brainstorm.

Phase 1: Resolve Mode

Check existing files:

• If design/gdd/game.md or design/gdd/systems-index.md missing → hand off: tell the user to run /gat-brainstorm [hint] first. Stop.
• If design/art/art-direction.md missing → hand off: tell the user to run /gat-brainstorm [hint] to establish global art direction. Stop.
• If argument matches a system name in systems-index.md → Mode: system

With game.md, systems-index.md, and art-direction.md present, assess completeness:

• Any system in systems-index.md lacks a GDD → Mode: continue
• Any system in systems-index.md lacks an art doc → Mode: continue
• All of the above are present → report design is complete, stop

Phase 2: Execute

Read templates:

• .claude/docs/templates/design/system-gdd.md
• .claude/docs/templates/design/system-art.md
• .claude/docs/templates/design/content-data.md

Also read existing design/narrative/*.md when present and pass relevant narrative context to spawned agents. Do not create or rewrite narrative docs here; use /gat-story for that.

Continue mode

Step 1 — For each system in systems-index.md lacking a GDD, in order:

Spawn gat-designer → design/gdd/<system>.md:

• Pass game.md, systems-index.md, system-gdd template
• Pass existing system GDD if present

Step 2 — Content Fill (for systems with high content volume)

For each system whose system GDD is complete AND which requires substantial content data, spawn gat-designer to write design/content/<system>-data.md:

• Pass the system GDD, game.md, systems-index.md, content-data template
• Pass existing content doc if present
• The content doc fills specific instances, parameters, sequences, and groups — the data that instantiates the rules defined in the system GDD

A system needs a content-data doc when its GDD defines data structures that need many concrete instances (e.g. an enemy GDD defines enemy attributes → content doc fills 25+ specific enemies; a stage GDD defines wave scheduling → content doc fills wave-by-wave scripts for all 5 stages).

Systems that are purely mechanical (e.g. input, tbs-scoring) typically do NOT need content-data docs — their parameters fit within the GDD itself.

Step 3 — For each system in systems-index.md lacking an art doc, in order:

Spawn gat-artist → design/art/<system>-art.md:

• Pass game.md, art-direction.md, the system GDD, the content-data doc (if it exists), system-art template
• Pass existing system art doc if present
• The artist now has both the GDD (rules/schema) and the content-data doc (specific instances) to design complete visuals

System mode

Require design/gdd/game.md and design/gdd/systems-index.md.

Step 1 — Spawn gat-designer → design/gdd/<system>.md

Step 2 — If the system needs content data, spawn gat-designer → design/content/<system>-data.md

Step 3 — Spawn gat-artist → design/art/<system>-art.md:

• Pass game.md, art-direction.md, the system GDD, the content-data doc (if it exists), system-art template
• Pass existing system art doc if present

Phase 3: Review

Summarize what was created or updated.

Use AskUserQuestion:

• Plan milestones (Recommended) → Run /gat-milestone
• Add another system → Run /gat-design <name>
• Stop here