SUBSTACK VERSION

Make a 3D browser game with Claude Opus 5.5 in a weekend

Build an original 3D game anyone can play, just by talking to the agent

This week @xikhar posted a browser game where you swing across a city, made with Claude Opus 5.5, Blender and an image model, and it pulled 1.55M views on X. After reading this, you can make your own original 3D game the same way: a character built in Blender, one fun move, three deliveries against a clock, and a link anyone can play in desktop Chrome. It takes Claude Code or Cursor on a paid Claude plan, an image model and a weekend. The agent writes all the code.

[Image 01: 01-repro-final.png] Line & Lantern at dusk: a courier in a rust-red coat swinging on a glowing line toward a ferry

That's Line & Lantern, my game from these steps, built in 64 minutes. A test script is at the controls.

[Embed post: https://x.com/xikhar/status/2104001664793600012]

His caption says it was his third attempt, with Opus at medium effort. Asked why it looks finished, he replied: "It’s because I gave reference images so it knew to keep working till quality is matching."

That's the method: the agent screenshots its own work and fixes it until it matches your picture. It can't feel the game, though. On body animation he wrote that "it can’t completely verify they look good so I need to give feedback each time." You judge the feel; the agent does the rest.

He hasn't published his prompt, and neither have the others here. The messages below are mine, shortened from the longer briefs I actually ran.

What you need

Big numbers in viral captions are API prices, not bills.

[Embed post: https://x.com/dangreenheck/status/2102878170089169235]

@dangreenheck's caption says "$1874.40 of Opus 5.5 tokens". His reply: "That's the API cost. I only paid $200 for the month."

01. Give the agent a way to check its work

The agent can only fix what it can see, so first give it a game page it can screenshot and check on its own. The rules go in CLAUDE.md, a file Claude Code rereads at the start of every session.

Set up a 3D browser game called Line & Lantern with three.js, and a way to check it yourself: open it in a headless browser, screenshot it and fail on any error. Show me one lit box. Write our rules in CLAUDE.md: medium effort, one district, a hero from a Blender script you run, and if a picture I owe you is missing, stop and ask. Body animation is my call, so show me and wait.

Look at the screenshot yourself, because a passing check only means no errors. If it's black, ask the agent to use your installed Chrome.

02. Describe your game on one page

Every session starts by reading one page about the whole game, so the agent doesn't drift into something bigger. Invent the game, or you'll get a copy.

Write a one-page brief for Line & Lantern and a three-session plan, but don't build anything yet. At dusk, a courier in a rust-red coat swings on a silk line between cranes and roofs in an invented harbor, delivering three packages in three minutes. Hold the mouse on a hook to swing and let go to fly; a 12-meter gap is crossable, a 30-meter gap isn't. Everything is original: no masked hero, no real city, no logos. End with "Actually test the finished result in a desktop web browser."

You get a brief and a plan: the swing, then the look, then the game. Cut anything bigger than one district. The brief's last line comes from @MengTo.

[Embed post: https://x.com/MengTo/status/2102760783344189761]

His shared prompt is almost 9,000 characters, and he says it still took "lots of steering. no pun intended."

03. Make a picture of the game you want

The agent builds toward a picture, so make one first in your image model, of something a browser game can actually draw.

An in-game screenshot from a stylized low-poly 3D browser game: a courier in a rust-red coat mid-swing above a wet cobblestone quay, a glowing silk line running from the left wrist to an iron hook on a dock crane. Chunky simple shapes, flat-shaded surfaces with soft gradients, warm bloom on paper lanterns, golden-hour sun from the left, a dark teal harbor. No text, no logo, no UI, no watermark.

[Image 02: 02-target-v2.png] The target picture: a low-poly courier mid-swing, the line running from the wrist to a crane hook, lanterns and a lighthouse at golden hour

The style words do the work. Without them, my first try came back as a photograph of a courier walking, with the line holding cargo. Save the picture into your project and tell the agent where it is.

04. Build the swing first

The swing is the whole game, so session one builds nothing else.

Start session one and build only the swing, on grey boxes: two roofs, a crane with three hooks, a pier, water, and a capsule for the courier. Clicking a hook fires a real rope that swings the courier like a pendulum, and letting go keeps the speed. Add a test that holds a click on a hook for two seconds, and it isn't done unless the courier moves more than 3 meters. Save your work and stop.

The usual miss is a line that's drawn and animated but moves nothing, hence the movement test. If the agent stops early, resend the open items two or three times at most, as Anthropic's Opus 5.5 prompting guide advises. Still no swing? Start over and ask for a real rope simulation.

05. Add the hero and match the picture

To match your picture, first make four square textures in your image model (cobblestone, brick, roof tiles and dock planks), each flat and tileable, seen from straight above, with even light and no text.

Session two: make the game look like my picture. Write a Blender script for an original courier with a long rust-red coat, a satchel and a wrist spool, with four moves (idle, run, swing, land), and attach the rope to the spool. Use my four textures and blend their edges so they tile. Then screenshot a swing, score it against my picture out of 10, and fix the weakest part until it scores 8. If the score stops rising for two rounds, show me and ask.

[Image 03: 03-hero-poses.png] The courier from one Blender script in four poses: idle, run, swing and land

@xikhar says Opus "models and rigs the Skelton in blender", but he hasn't published that script. The scoring loop is a shortened version of Dream Loop Pro.

06. Play it yourself

This is the one step the agent can't do. Play one delivery yourself, then tell the agent what you noticed.

I played one delivery. Here's what felt slow, what looked wrong and what I want next: (your three sentences). Fix only those, don't add features, and check it again.

[Embed post: https://x.com/DannyLimanseta/status/2104215873120764032]

That's how @DannyLimanseta built Wildbrush with his boys: "They tell me what they want in their game and I prompt it into Opus 5.5 to build it." Don't start session three until a person can cross one gap on purpose.

07. Finish the game and share it

Session three turns the swing into a game you can win or lose, and packs it for the web.

Session three, keeping my fixes: add three drop pads in order with the next one glowing, a three-minute timer, and pier lanterns that dim as time runs out. Water sends you back to the last pad. Teach the move in the first 10 seconds with one glowing hook ahead and the words "Hold click on a glowing hook." Then make a build I can upload that loads with no errors, plus a readme with the controls and "Original work. Not affiliated with any existing game."

You get a folder to upload to Vercel, GitHub Pages or Cloudflare Pages, or zip for itch.io.

[Embed post: https://x.com/JaydenDavisNC/status/2103357848961036304]

@JaydenDavisNC says InkWave was "ENTIRELY built in two days". It has the shape to copy: one move, an original name, and a page a stranger can finish. Play it here.

All six messages, on one card:

[Image 04: 04-cheatsheet.png] Cheat sheet: the six messages to the agent in order, from setup to sharing the finished game

What I got

I ran an earlier version of these steps in Cursor with Claude Opus 5.5 and a gpt-image model, without setting an effort level or tracking the cost. The build took 64 minutes.

Within 15 minutes the Blender script was exporting the hero, and before the half-hour mark a held click swung the courier almost 30 meters. The score against my picture rose from 4.8 to 6.5 and stalled there, so the stop rule ended the run soon after the first win.

Nobody played it by hand. A test script made all three deliveries in about half a minute without touching the water. Its first 20 seconds, uncut:

[Video 05: 05-repro-gameplay.mp4] The test script's first 20 seconds, uncut: a rooftop drop, a few swings and the ferry delivery

I also cut corners: nobody tried the swing before session three, the session that built each frame also scored it instead of a fresh one, and the coat never got a texture.

[Image 06: 06-repro-glare.png] Still wrong in the final build: the body swings nearly horizontal, sun glare washes out the left side, and there's too much bloom

The core held up: one move, an original name, a way to win and lose, and a build that loads with no errors. The body motion didn't. When you post yours, say how long it took and what's still broken.

Making money from it

No post above shows an invoice, so these are published asking prices. Studios buy playable ads: EXYZ asks $450 for one on the client's art, delivered in 2 to 3 working days, and FrontFrog's packages start at $1,250, with the top tier from $4,500. Poki pays 100% on players who find your game themselves and 50/50 on players it sends you, with a five-year exclusive by default, terms it calls indicative, and it warns that "AI art doesn't make a clone original." itch.io sells to players directly and takes 10% by default. My suggestion is to sell a playable ad first: quote $450 to $4,500 for one mechanic in both phone orientations, under 5 MB, with three revision rounds and the source on the last payment.

Credits

View counts are as of Sep 28.