Create this in a new sub folder. /goal Create the most impressive demo of Opus 5.5 (you) capabilities to be shown off on Twitter. Pick what you want to make, record it into a short video that can get attention, and have fun.
Make it yours. Keep "/goal" and replace the sentence after it with your own goal. The model picked the demoscene on its own from "Pick what you want to make", so name a form there if you want something specific.
Demoscene film from a single HTML file
A 43-second demoscene film, "Ex Nihilo", in which every pixel and sound comes from one 280 KB HTML file: raymarched shader scenes from a light echo to a black hole, scored by a JavaScript synth. Claude Code chose the idea itself from a one-line goal.
“I asked Claude Opus 5.5 to make the most impressive demo of itself and gave it zero direction.”
- Claude Code
- Claude Opus 5.5
- WebGL2
- Plain JavaScript
- FFmpeg
- One-shot
- 4h 52m
- 697M tokens
You'll need
- A large usage allowance; the run hit usage limits twice
- Chrome with GPU access and FFmpeg for the offline render
How it was made
One prompt, plus "continue" whenever a usage limit reset. Run with ultracode, which the creator believes is xhigh effort. Claude built its own engine, build script, and still renderer first, then ran five scene agents and a composer in parallel, with critic agents re-rendering and scoring each scene.
697M tokens processed (98.1% cache reads) and 566K output tokens across 36 agent runs
Posted Sep 23, 2026 · X · 1.6k likes · 130k views · 103 comments
Prompt from: Reply on X; the creator's write-up quotes the goal sentence as "the entire prompt"
Look notesby Reference
Six raymarched scenes, each with a single subject on black: a star inside glowing dust shells, a liquid chrome blob, an iridescent fractal crystal, snowy peaks at dawn, a neon grid city, and a black hole, ending on a typeset title card.
- Color
- Mostly black, with one dominant tone per scene: white starlight, chrome gray, rainbow bismuth on warm gray, dawn blue and peach, neon magenta and cyan, and orange-gold for the accretion disk.
- Type
- Small lowercase monospace captions ("every pixel. every sound. one html file", "03 CITY" with a technique note) and a thin, widely spaced EX NIHILO title over a faint wall of tiny source code.
- Framing
- 16:9 with centered subjects and deep black space around them. The city and tunnel shots use one-point perspective down a street of neon blocks.
- Sound
- A score from a synthesizer written in plain JavaScript in the same file, mixed by measurement to -14.3 LUFS, according to the creator's write-up.
- Structure
- Light echo with the opening caption, chrome blob, fractal crystal, mountain range, neon city street, a tunnel with a circular portal, the black hole, a lone point of light on black, then the EX NIHILO end card.
