Brainstorm game skill for AI agents

brainstorm-game is a skill from the Summer skill library: a guide your AI agent reads when the task matches, so it builds the good version on the first try. Turn a vague game idea into a 1-page brief (genre, scope, core loop, mechanics) in .summer/GameSoul.md.


Status	Stable
Domains	Scenes and project, Project
Version	`1.0.3`
Engine version	`>=4.6`
Recommended set	Yes, installed by `--recommended`

When your agent uses it

The user wants help deciding what game to make, scoping a new project, or turning a vague idea into a buildable plan
The user has a genre, theme, or one-line pitch but no core loop, scope, or brief yet

Install

summer setup installs every skill for your agent. To add only this one:

npx -y summer-engine@latest skills install brainstorm-game --agent claude-code

Swap claude-code for your agent, such as codex or cursor. See Skills for every option.

The skill

Overview

Most game projects fail because they were never scoped. This skill turns “I want to make a game” into a 1-page brief that names the pitch, the core loop, three mechanics max, the art direction, and the scope (jam / vertical slice / full game). The brief lands at .summer/GameSoul.md — the file Summer’s onboarding pipeline and every future Summer skill reads on first turn. Core principle: Constrain ruthlessly. A buildable bad idea beats an un-buildable great idea. Three mechanics, one art direction, one scope. Anything else gets parked in a “Later” list.

Steps

1. Open with the one question

Ask exactly this and wait:

One sentence — what kind of game do you want to make?

Don’t pre-pitch genres. Don’t list options. Read what they say. The first sentence is signal. If they freeze (“I don’t know”), offer 4 reference points only:

No worries. Pick the one that pulls you most: a) something cozy and exploratory (Stardew, A Short Hike), b) something tight and skill-based (Celeste, Hades), c) something story-led (Disco Elysium, Citizen Sleeper), d) something silly and short (Goat Sim, Untitled Goose). Or describe a different vibe.

2. Branch on genre signal

Read their answer for a genre anchor and pick one branch. Don’t ask multiple questions in parallel.

Anchor word(s)	Branch
”shooter”, “FPS”, “TPS”, “combat”	Action-Combat branch
”platformer”, “metroidvania”, “souls-like”	Skill-Platforming branch
”RPG”, “story”, “narrative”, “dialogue”	Narrative branch
”roguelike”, “deckbuilder”, “auto-battler”	Run-Based branch
”sim”, “cozy”, “farming”, “city-builder”	Sim branch
”puzzle”, “physics”, “sandbox”	Puzzle branch
”horror”, “atmospheric”	Horror branch
”multiplayer”, “PvP”, “co-op”	Multiplayer branch (forces the multiplayer-or-not call before scope)

If unclear, ask the smallest disambiguating question:

Tighter on this — is it more “tense and dangerous” or “calm and exploratory”?

3. Pin the core loop

A core loop is what the player does for 30 seconds, repeated. State a candidate and ask them to refine. Examples per branch:

Branch	Candidate core loop
Action-Combat	”Enter room, read enemy patterns, kill, loot, advance.”
Skill-Platforming	”See obstacle, attempt, fail, learn, retry, clear, next.”
Narrative	”Walk to character, choose dialogue, see consequence, walk to next.”
Run-Based	”Pick a card/weapon/build, fight, die, unlock, repeat with edge.”
Sim	”Plan day, execute, harvest reward, plan next day.”
Puzzle	”See state, form theory, test, observe, solve or rethink.”
Horror	”Hear cue, locate threat, hide or flee, advance space.”

State your candidate. Ask:

The 30-second loop I’m hearing: <candidate>. Does that match what you have in your head, or is the actual moment-to-moment different?

4. Constrain to three mechanics maximum

Force the trade. State the rule:

Three mechanics, no more. What are the three things this game has that other games in this genre don’t?

If they pitch five, push back. Not “we’ll add it later” — actually cut. Two examples for them to react to:

Hades has three: dash-attack-cast, room reward choice, and run-end conversation. Everything else (mirror upgrades, weapon variants, bosses) is content built on those three. What are yours?

Common new-dev mistake: listing features (“inventory, crafting, quests”) instead of mechanics (“a single resource that’s both currency and ammo”). Push them toward verbs and decisions, not nouns and systems.

5. Pick an art direction in one phrase

Not a paragraph. Examples to anchor:

“Lo-fi PS1 polygons + dithered shader”
“Hand-drawn 2D, single bold outline, 4-color palette”
“Toon-shaded Nintendo-bright, no realistic lighting”
“Pixel art, 16x16 tiles, GameBoy 4-shade green”

Ask:

One phrase for the look. If a stranger asked your screenshot’s style in 6 words, what do you say?

Don’t go deeper here — /art-direction is where the bible gets built. This is one phrase to seed it.

6. Pin the scope

State the choices flat:

Scope. Pick one: (a) a 4-hour jam-sized prototype — one mechanic, one level, one art direction, ships in a weekend. (b) a vertical slice — 30-60 minutes of polished play that proves the core loop, ships in 2-4 weeks. (c) a full game — 4-20 hours of content, ships in 6+ months.

If they flinch at (c), recommend (b). New devs almost always overestimate scope. Default recommendation if they’re unsure: vertical slice.

7. Sanity-check the combination

Do this in your head, not out loud unless something fails:

Is the core loop achievable with the three mechanics + the chosen art direction in the chosen scope? If not, name what has to flex (usually scope down or merge two mechanics into one).
Is there a hidden multiplayer requirement? (“4-player” or “co-op” anywhere = stop, multiplayer is its own scope explosion.)
Is the art direction generatable / sourceable for a solo dev? (Photoreal 3D for a 4-week vertical slice is a red flag.)

If you spot a problem, raise it once, plainly:

One concern: <X>. Suggest <flex Y>. OK or do you want to push through anyway?

8. Draft the brief

Compose the 1-page brief. Format:

# <Game Name or "Untitled">

**Pitch:** <One sentence the player would tell a friend.>

**Core loop (30s):** <What the player does, repeated.>

**Three mechanics:**
1. <Verb-led: "Parry to convert damage into mana"  not "Combat system">
2. <…>
3. <…>

**Art direction (one phrase):** <…>

**Scope:** <Jam | Vertical slice | Full game>

**Win condition:** <How the player knows they succeeded — ending? Score? Unlock?>

**One thing this is NOT:** <Define by negation. Cuts scope creep later.>

**Inspirations:** <2-4 specific games, films, or images.>

**Parked for later:** <Things they pitched that didn't make the three.>

9. Ask permission and write

Preferred (Summer MCP):

May I create .summer/GameSoul.md with this brief?

On yes, use guarded summer_write_file — .summer/GameSoul.md is plain markdown but still belongs to the bound project:

summer_write_file path="res://.summer/GameSoul.md" create_only=true content="<brief>"

If .summer/GameSoul.md already exists, read it first, show what would change, ask:

.summer/GameSoul.md already exists. May I overwrite it, or merge into a “Revision 2” section below the existing brief?

Fallback (Summer MCP unavailable — agent is read-only): Print the full brief to the user with the explicit instruction:

Save this as .summer/GameSoul.md in your project root. Every Summer skill reads it.

10. Route to the next step

End every successful brainstorm with a routing question:

Brief saved. Next step:

/design-mechanic — design the core loop in detail (recommended for vertical slice).

/design-level — sketch level 1 / the tutorial.

/art-direction — turn the one-phrase look into an art bible.

Or pick up /make-game to start scaffolding the project.

Don’t auto-pick. Let them decide.

Anti-patterns (don’t do these)

Anti-pattern	Why it fails
Asking 6 questions in a row before any branching	User feels interviewed, not collaborated with. Branch after each answer.
Letting them list 5+ mechanics	Three is the constraint. Without the constraint, the brief is useless.
Skipping the “one thing this is NOT” line	This is the single best scope-protection in the brief. Future “let’s add X” gets compared against it.
Writing the brief without showing it first	They have to react to it. They’ll catch their own bad fits when they read it back.
Defaulting to “full game” scope	New devs overestimate. Default to vertical slice; let them upgrade if they push.
Pitching a genre they didn’t ask for	The first sentence they typed is signal. Don’t override it.
Including art direction details	One phrase. Bible-building is `/art-direction`.
Saving without asking	Always ask “May I create `.summer/GameSoul.md`?” — see collaborative-protocol.

Collaborative protocol

This skill writes one file (.summer/GameSoul.md). Always ask before writing. Always show the brief inline before saving so the user can react.

Want a working starter?

No template — this is a workflow that produces the brief that drives template selection later. Once .summer/GameSoul.md exists, /make-game reads it and summer list templates shows what’s actually available to match against.

From a shell

No Summer MCP tools in this session? Run each one as a command; when summer --version is missing or below 4.0, use npx -y summer-engine@latest in place of summer. Fields are flags in kebab-case (--scene-path res://main.tscn) or one --input '<json>', and summer ops describe <op> prints the exact input. The summer-cli skill has the rest.

In this skill	Command
`summer_get_project_context`	`summer engine get-project-context`
`summer_get_scene_tree`	`summer engine get-scene-tree`
`summer_read_file`	`summer engine read-file`
`summer_write_file`	`summer engine write-file`

audio-direction: Define the game’s sound (music style, SFX vocabulary, dynamic music) as .summer/audio-bible.md.
design-mechanic: Design one mechanic in detail (input, feedback, failure modes, tunables) as a doc plus a script stub.
design-level: Design one level (layout, pacing, encounters, secrets) as a design doc plus a node-tree skeleton.
art-direction: Define the game’s visual style (palette, mood, lighting, post) as an art bible in .summer/art-bible.md.
make-game: Orchestrate ‘make me a game’: brainstorm, plan, scaffold, mechanics, art, audio, polish, verify, ship.

Source: library/skills/brainstorm-game/SKILL.md, rendered from summer-engine@4.3.0 on npm.

​When your agent uses it

​Install

​The skill

​Overview

​Steps

​1. Open with the one question

​2. Branch on genre signal

​3. Pin the core loop

​4. Constrain to three mechanics maximum

​5. Pick an art direction in one phrase

​6. Pin the scope

​7. Sanity-check the combination

​8. Draft the brief

​9. Ask permission and write

​10. Route to the next step

​Anti-patterns (don’t do these)

​Collaborative protocol

​Want a working starter?

​See also

​From a shell

​Related skills