Moonlit Courier

Auto-run across lantern-lit rooftops, hold to leap higher, and post the night's letters at the mailbox.

Three.js4 build stagesComplete game available

Make it yours ↓Play full game ↗

Local build pack · No model call starts on this page

THE GAME LOOP

A small idea worth finishing.

Auto-run with one jump: tap for a hop, hold for a capped higher leap, with 100 ms buffer and coyote time
Three hearts: a gap fall respawns on the last safe roof, an obstacle hit gives a short blinking recovery
Hand-placed ~60 s route in three acts, with clearly more letters than the mailbox needs

THE LOOK & FEEL

A world with its own personality.

Navy sky, large pale moon, layered town silhouettes, warm lit windows and soft lantern pools
Primitive-built cat with readable run, jump stretch, springy landing and trailing scarf
Wide side view in landscape, 3/4 chase view in portrait, framed so the next hazard is visible

MADE FOR THUMBS

Plan the phone experience first.

Tap anywhere or the big thumb Jump button; hold for a higher, capped leap. Pause sits top-right. Portrait swaps to a 3/4 chase camera.

The playbook requests H5 layouts and input. Real-device playtesting is still part of the build.

01 / MAKE IT YOURS

Same spark. Your world.

Change a few details. The brief and every build stage update together.

Your main characterYour worldWhat the player wants to achieveA personal touch Optional

02 / YOUR BUILD PLAYBOOKThree.js direction

Create an original hand-authored rooftop runner as one self-contained browser game in Three.js (WebGL2). The player is a small black-and-cream cat courier with a coral scarf crossing an amber-lit rooftop town at blue hour. Goal: collect at least 8 letters and reach the mailbox in about 60 seconds.

Core loop: the courier auto-runs and one action jumps (tap, click, Space or Up). A tap gives a low hop; holding up to about 0.2 s gives a higher, capped leap. Add a 100 ms jump buffer and 100 ms coyote time. Hand-place a ~60-second route in three acts (warm-up roofs, a lantern quarter, a final bridge) where every gap and knockable obstacle sits inside the jump envelope and is visible before it matters. Three hearts: a gap fall respawns on the last safe roof; an obstacle hit costs a heart and grants about a second of blinking recovery. Place clearly more letters than required.

Open on a living title scene with one Play button and a small controls hint. In play show only hearts, letters/progress and pause. End with letters, route time and Play again. Keep rules in a deterministic fixed-step module separate from rendering, and use procedural meshes and textures only.

The full pack adds the H5 controls, build contract and acceptance checks.

Copying, downloading and customizing are free. No build starts here.

Read the full local build pack

# Moonlit Courier — SiGameGen original game brief

Prompt template, not a prebuilt game. Engine direction: Three.js.

## Project brief

Create an original hand-authored rooftop runner as one self-contained browser game in Three.js (WebGL2). The player is a small black-and-cream cat courier with a coral scarf crossing an amber-lit rooftop town at blue hour. Goal: collect at least 8 letters and reach the mailbox in about 60 seconds.

Core loop: the courier auto-runs and one action jumps (tap, click, Space or Up). A tap gives a low hop; holding up to about 0.2 s gives a higher, capped leap. Add a 100 ms jump buffer and 100 ms coyote time. Hand-place a ~60-second route in three acts (warm-up roofs, a lantern quarter, a final bridge) where every gap and knockable obstacle sits inside the jump envelope and is visible before it matters. Three hearts: a gap fall respawns on the last safe roof; an obstacle hit costs a heart and grants about a second of blinking recovery. Place clearly more letters than required.

Open on a living title scene with one Play button and a small controls hint. In play show only hearts, letters/progress and pause. End with letters, route time and Play again. Keep rules in a deterministic fixed-step module separate from rendering, and use procedural meshes and textures only.

## Local build contract

Work in a new isolated project directory through my signed-in local Claude Code subscription. Do not call a separate model/image API, change provider settings, use an API gateway or spend on a paid service. Do not deploy, publish, commit or push without an explicit follow-up instruction. Read applicable repository instructions first.
Build a complete browser game with the full campaign and progression in the project brief. Keep the rules-first stage as development work, then finish the art, game feel and release review before calling the game complete. Include an interactive skippable tutorial, distinct data-driven levels or missions, meaningful progression, fair failure and chapter retry, a final ending, settings and replay. Pin locally installed dependencies; bundle code, engine, fonts and assets into a self-contained HTML. Use original procedural art or supplied assets with permission and keep a licence inventory. Separate deterministic rules, input, renderer, UI, audio and scene data.
SiGameGen embed contract: opaque-origin iframe, no runtime CDN/imports, fetch/XHR/WebSocket, browser storage, popups or page navigation. Keyboard and touch must work without pointer lock on phones. Emit only integer points: parent.postMessage({type:'sigamegen:game-event',version:1,event:'started',score:0}, '*') once per run, and the same schema with event:'game_over' and the final score once at win/loss. Points are not money.
Save campaign checkpoints through the host only. Request {type:'sigamegen:save-request',version:1,gameId:'<game-id>'}; accept {type:'sigamegen:save-state',version:1,gameId,state,storage:'available'|'unavailable'} only from window.parent. Validate your actual save schema, own-key IDs and ranges. Post {type:'sigamegen:save',version:1,gameId,state} with a small plain JSON state (<=8192 UTF-8 bytes); state:null explicitly clears it. Show saved only after {type:'sigamegen:save-status',version:1,gameId,status:'saved'|'cleared'|'unavailable'|'invalid'} from the parent. Failed or missing acknowledgements must stay honest and allow retry; missing storage must not block play. Local progress and scores never authorize money or rewards.
Audio is off until opt-in. Support volume, reduced motion, safe areas, controls at least 48px, portrait/landscape camera fit, pointercancel, pause/restart confirmation, tab hide and return without fast-forward. Tutorial hints must leave the action visible, and primary actions must fit short landscape screens. Stop rendering while paused, hidden and on results; cap particles/enemies and mobile DPR at 1.5. Target <=1.6MB raw / 400KB gzip; measure the actual result, not a promise. Test actual game fairness, legal-input progression, loss/retry and save validation; then review the full campaign, upgrades, ending and replay in the real sandbox at 320x568, 393x852, 852x393 and desktop. Keep inspection bots and debug controls out of release builds. Report passed checks and untested device/audio paths separately.

## Continue in the same Claude Code project

### 1. Core mechanics

Build the playable vertical slice before any final art. Implement the deterministic rules module: fixed timestep, jump physics with buffer and coyote time, hearts, respawn on the last safe roof, letters and the mailbox win/loss. Render an amber-lit rooftop town at blue hour as simple greybox roofs with a capsule stand-in for a small black-and-cream cat courier with a coral scarf. Author the route data by hand for collect at least 8 letters and reach the mailbox in about 60 seconds. Add start, pause, restart and end screens. Write tests proving every gap and obstacle fits the jump envelope with margin, a damage-free run exists, each respawn point is safe, and reset restores a pristine state. Write fresh code; do not reuse code or art from other projects.

### 2. Art pass

Replace the greybox with the art pass for an amber-lit rooftop town at blue hour: navy-to-indigo sky, a big pale moon, three depth layers of rooftops with warm lit windows, tiled roofs, chimneys, cables and lantern pools. Model a small black-and-cream cat courier with a coral scarf from primitives with ears, eyes, curved tail and scarf, and animate walk, run, jump stretch, falling reach and a springy landing. Keep obstacles high-contrast and telegraphed against dark roofs. Merge static geometry into chunks, cap lights (one moon light, a sky fill, a few pooled point lights) and draw textures procedurally. Keep a short licence note listing every dependency and asset source.

### 3. Game feel

Polish how it feels to collect at least 8 letters and reach the mailbox in about 60 seconds: landing dust, small speed streaks, a letter pickup arc into the HUD counter, 60-80 ms hit-stop and bounded camera shake. Use a wide side view in landscape and a 3/4 chase view in portrait, solving the framing so the next hazard is always on screen. Add opt-in synth audio (soft tune, jump, land, pickup, hit) behind a visible toggle, and a reduced-motion option that follows the OS setting and removes shake and streaks. Onboard on a calm first roof with a one-line hint so a small black-and-cream cat courier with a coral scarf is never in danger before the player has jumped once.

### 4. Review & ship

Review the a small black-and-cream cat courier with a coral scarf runner as a release candidate. Check portrait and landscape at narrow and wide sizes, safe-area controls at least 48 px, and that pointercancel or blur releases a held jump. Pause and hidden tabs must stop simulation and rendering, and returning must not fast-forward. Add a quality fallback (DPR cap, fewer particles) and a WebGL-unavailable screen. Confirm the build is one self-contained HTML with pinned dependencies and no runtime network, storage, popups or navigation, and that one started and one game_over event fire per run. Re-run the rule tests and list anything you could not verify.

## Acceptance checks

- A scripted or bot run proves the hand-made route can be finished without damage in roughly 55-65 seconds.
- Every gap and obstacle is clearable by the capped jump and is on screen well before contact in both portrait and landscape.
- A gap fall costs exactly one heart and respawns on the last safe roof; restart restores hearts, letters, obstacles and timers.
- Pause or a hidden tab stops simulation and rendering; resuming continues at normal speed with no jump stuck held.

## Research references

These are design references, not included code or assets. The prompts are original SiGameGen briefs. Model attribution in external repositories is creator-reported.

- CatWalk · blitast_studio: https://x.com/blitast_studio/status/2102775461701091531
  A cat-led night-runner showcase. The original post and playable demo were reviewed in our earlier research. Our game, characters and artwork are original.

Want a quick 2D sketch first?

The online builder adapts these mechanics to Canvas 2D. The full Three.js version is built in your local Claude Code project.

Open a 2D sketch ↗Opening the builder is free. Only confirming Build game uses platform credits.

DONE MEANS PLAYABLE

The checks this game should pass.

A scripted or bot run proves the hand-made route can be finished without damage in roughly 55-65 seconds.
Every gap and obstacle is clearable by the capped jump and is on screen well before contact in both portrait and landscape.
A gap fall costs exactly one heart and respawns on the last safe roof; restart restores hearts, letters, obstacles and timers.
Pause or a hidden tab stops simulation and rendering; resuming continues at normal speed with no jump stuck held.

These are requirements for your future build, not results already verified for this prompt.

RESEARCH, WITH CREDIT

What shaped this playbook.

Original SiGameGen prompts authored in our local Claude Code subscription session. References inform the design; their code, assets and prompts are not bundled. External model attribution is creator-reported.

CatWalk · blitast_studio ↗

A cat-led night-runner showcase. The original post and playable demo were reviewed in our earlier research. Our game, characters and artwork are original.