Tutorial · a real build, start to finish

One sentence in.
A whole game out.

This is the exact journey a real prompt took through this site — every step below is something you can try yourself, and the game at the bottom is the actual product it produced. Nothing here is a mockup.

1Say it2We ask, you tap3The prompt, sharpened4Research + the frozen checklist5Tested, then playable

Step 1 · The raw prompt (all a person typed)

Lowercase, no punctuation worth mentioning, seventeen words of pure vibe. This is a normal prompt — it's also missing almost everything a builder needs to know.

make a side-scrolling game like sonic but ai themed, easy to play, boss battle, stars to collect, a couple secrets, midi soundtrack

Try step 1 with your own idea →

Step 2 · The questions it was FORCED to answer

No skipping — these answers are the difference between “a game, sort of” and a game someone can actually finish. (On /start you answer the same kind of questions by tapping.)

Who is it for?	Anyone — first-time players, on a phone or a keyboard.
How hard?	Easy and forgiving: 5 hearts, checkpoints, a fall costs a heart and a short walk — never a full restart.
Controls?	Keyboard AND on-screen touch buttons.
What do you collect?	Stars — placed singly and in arcs that teach the jump.
The boss?	One boss at the end. Telegraphs its attacks, beatable by a brand-new player.
Secrets?	Exactly two: a breakable wall hiding a Star Vault, and a hidden spring to a sky route.
Sound?	An original MIDI-style chiptune loop synthesized in code, with a mute button.
Tech limits?	One HTML file. No downloads, no images, no licensed anything — everything drawn and played in code.
Done looks like…	Playable start to finish in the browser; the win screen reports stars, secrets, and time.

Step 3 · The refined prompt — frozen, word for word

The answers above were assembled into this spec, and then it was frozen: once building started, this text did not change. The game below was built from exactly these words — copy them and give them to any AI and you should get a sibling of the same game.

Build 'Prompt Runner', a single self-contained HTML file (no external assets, no dependencies, all art drawn in code on canvas, all music synthesized in code) containing an AI-themed side-scrolling platformer in the style of classic 16-bit momentum runners. Player: a small agent bot with momentum running, a rolling spin move, variable-height jumps, coyote time, and animated code-drawn sprites. World: a tile-based level (tile grid generated from a heightmap plus placed platforms, ramps, springs, one-way platforms, checkpoints) with at least three parallax background layers scrolling at different rates, and a loop-the-loop segment the player runs through at speed. Collectible: stars, placed singly and in arcs, with an on-screen counter. Enemies: 'glitch bugs' that patrol platforms — jumping on them or rolling into them destroys them; touching them any other way costs one heart. Difficulty: easy and forgiving — 5 hearts, checkpoints, falling in a pit costs one heart and respawns at the last checkpoint, never a full restart. Boss: at the end of the level, a rogue 'Unbounded Core' with 6 hit points, telegraphed attack patterns (warning first, then a ground beam, spawned minions, or orb shots), and a clear vulnerable window when it dips; beatable by a first-time player. Secrets (exactly two, both tracked and reported on the win screen): (1) a breakable wall, destroyed only by rolling into it, hiding a Star Vault room full of stars; (2) a concealed spring that launches the player to a sky route with a star cluster and a bonus heart. Sound: an original MIDI-style chiptune loop (square-wave lead, triangle bass, noise hats) synthesized with WebAudio, starting only after the first user interaction, with a working mute. Controls: arrow keys / A,D to move, Space / W / Up to jump, Down / S to roll, M to mute, plus on-screen touch buttons for move, jump, and roll. Screens: a title screen with plain instructions, a HUD (stars, hearts), and a win screen reporting stars collected, secrets found, and time. Performance: requestAnimationFrame loop, no per-frame allocation in hot paths, plays smoothly at 60fps on a mid-range phone.

Step 4 · Research first — and an honest “no pack”

Before building, the harness's research tools were asked — live, over this site's own MCP — for a known-good pattern for “2D canvas platformer in a single HTML file.” The tools answered plainly:

research_dispatch → { "fallback": "crawl", "labelled": true, "reason": "no use-case matched above threshold", "candidates": [] }

Translation: the curated research packs cover payments, Google sign-in, MCP servers, and booking — not game development — and the tool said so instead of making something up. That's the behavior the harness is for. The game was therefore built from platform knowledge, with the frozen checklist (step 5) doing the guarding a pack would normally help with. A game-dev pack is the obvious next curation.

Step 5 · The checklist it was graded against

Written before the build, run against the finished build (11 criteria, 23 automated probes — a probe suite, not a vibe). Full test file ships in the project: scripts/test-prompt-runner.mjs.

Loads standalone, zero console errors, canvas renders real pixels	PASS — 354 distinct colors sampled from the live canvas
Player moves with momentum; jump works (variable height, coyote time)	PASS — ran 407px under held input; jump apex measured
Three-plus parallax layers + a tile-based level	PASS — scroll factors 0.15 / 0.35 / 0.6 + hills, tile grid from a heightmap
Star pickup increments the counter (47 stars in the level)	PASS — counter rose on probe runs
Secret 1: rolling breaks the cracked wall into the Star Vault	PASS — found by the probe, playing the real input path
Secret 2: concealed spring launches to the sky route	PASS — launch measured, secret flag set
Pit fall = −1 heart + checkpoint respawn (never a full restart)	PASS — respawned at checkpoint, run alive
Boss spawns, telegraphs, takes damage only in its vulnerable window	PASS — HP 6 → 0 across 6 real hits
Soundtrack graph builds on first interaction; mute toggles	PASS — WebAudio running, mute on/off verified
Win state reachable start-to-finish	PASS — scripted full playthrough reached the win screen
No external assets anywhere in the file	PASS — no script/link/img tags, no remote URLs, no audio files

Honesty footnote, where it belongs: the first probe round failed 3 checks (the loop-the-loop spun the wrong way, two “pits” had invisible floors, and the star pickup radius was too tight). One bounded repair round fixed all three; the re-run is the 23/23 above. The failures are documented in the build log, not edited away.

Step 6 · Play the product

Prompt Runner. Bit, a little agent bot, vs. the rogue Unbounded Core. Arrows / A,D to move, Space to jump, ↓ to roll, M for music. On a phone, the buttons appear on the game. Two secrets are in there — the wall by the Checkpoint Hills looks cracked, and something glitters above the bushes…

▶ Play full-screen⬇ Download the file

The whole game is one HTML file — no images, no audio files, no libraries. Copy it, download it, open it offline: it just works. That's what “done” looked like for this prompt.

✍️ Now start yours →Open the workspace (agents, reviews, the ledger)

One sentence in.A whole game out.