Tantrum is a Chrome extension I have been building that turns the web page in front of you into a toy. You can wreck it, mend the cracks with gold, grow a garden over it or doodle on it, and Esc puts everything back. Version 0.2.0 adds a fifth mode, Chaos Mode, where a small black cat does all of that for you. This post is about the cat: how it decides what to do next, how its hammer swing was made to look cute, and how I checked whether watching it is any fun. Tantrum is not on the Chrome Web Store yet; the listing is in preparation.
What is Tantrum?
Click the Tantrum button on any ordinary website and a small toolbar appears with four hands-on modes, plus Chaos Mode. Rage shoves, hammers, sets fire to and shatters things, and Smash knocks the letters out of a word. Mend puts knocked-off things back where they were and turns every crack into a gold seam. Wild grows morning glories, ivy, moss and mushrooms where you click. Doodle has paint, tape, a marker, bubble wrap and frost. That is 24 tools across four modes, and every change happens only in your own tab. The website is never touched, and reloading the page brings it back. The full tour and the privacy policy are on the Tantrum project page.
What does Chaos Mode do?
With Tantrum open, press T and a cat in a purple bandana walks onto the page. It picks a tool, walks to a spot, winds up and uses the tool there. Then it picks another tool, from any mode, and does it again. A few minutes in, the page is cracked, half mended in gold, overgrown and covered in tape. Every so often the cat reaches for Rewind and the page goes back to clean, and the build-up starts over.
Three rules kept it from being annoying. Every move the cat makes is exactly one undo step, so Ctrl+Z takes back one bonk rather than the last minute. It never aims under the Tantrum toolbar. And the moment you click, scroll or press a key, it stops and lets you take over. Its moves are also counted separately, so the cat cannot earn your badges for you.
How does the cat decide what to do next?
A small “director” runs the loop in the figure. It knows nothing about the page or the screen; it gets a random seed and the clock, which means the same seed replays exactly the same run. That made it testable: 17 unit tests drive it without a browser at all.
Picking a spot turned out to matter more than picking a tool. My first builds chose a random point on the page, and the cat spent a lot of its time walking long distances to do something that changed nothing, like brushing gold over a spot with no cracks in it. Two changes fixed most of that. The cat now looks at three candidate spots and goes to the nearest, and each tool aims at something it can actually change: the gold brush aims at things that are broken, and Smash aims at a word on a plain background. If a tool finds no target at all, it sits out until the cat’s next move lands. When a tool’s effect is still settling, like fire still spreading, the cat waits, but never for more than four seconds.
How do you make a hammer swing look cute?
The first version of the cat was a small chibi creature, and I did not like it. The one I kept is an upright black cat with a real arm: shoulder, elbow, wrist and a mitten paw, with the hand placed first and the elbow worked out from it (two-bone inverse kinematics), so the elbow bends the right way whichever way the cat faces. Drawn figures drift toward stick figures when joints are skipped, so the drawing code has to pass 11 automatic checks (joint order, limb lengths, which way each knee and elbow bends, mirroring when the cat turns around), and I made 19 deliberately broken versions of the rig to prove the checks catch each kind of mistake.
The cute part is timing more than drawing. The wind-up pulls the elbow and the weight back for about a quarter of a second, the contact pose holds for the first third of the recovery after the hit, so your eye catches the hit, the eyes squeeze shut on the bonk, and the follow-through overshoots a little before relaxing to idle. The mallet is a toy one, red and cream. The four frames below are drawn by the extension’s own renderer, converted to SVG for this page.
Is watching Chaos Mode actually fun?
I cannot measure fun, but I can measure the things that kill it: waiting, walking, and moves that change nothing. A playtest script lets the cat play three test pages in a real browser and records what a person watching would see. To make sure it could tell a dud from a real move, I also ran it once with the tools deliberately broken, and it reported them as duds.
In a run on September 25, 2026, the cat played each of three test pages for about 90 seconds. It made 44 or 45 moves per page, about 29 a minute, and its first move came 0.8 to 1.5 seconds after pressing T. It spent 24 to 32 percent of its time walking, and the longest stretch with nothing visibly changing was 3.8 seconds. One move out of 134 changed nothing: a Shine with no gold on the page yet to make glint. With the tools broken on purpose, 64 percent of moves came back as duds, so the detector is not simply saying yes. Earlier builds spent up to 46 percent of their time walking; looking at three nearby spots and aiming each tool at something it can change are what closed that gap.
What stays the same for you?
- Esc puts back everything Tantrum changed on the page, yours and the cat’s.
- Nothing leaves your browser. Tantrum makes no network requests, has no accounts and no analytics.
- It only runs on the tab where you clicked its button or pressed its shortcut, or on a site you switched Keep on for.
- With reduced motion switched on in your system, the cat moves slower and waits longer between moves.
When can I try Tantrum?
Version 0.2.0 is packaged and the Chrome Web Store listing is in preparation. When it is live, the store link will go on the Tantrum project page, which also has the full privacy policy. Until then, if you have a question about it, write to me at dhseadev@gmail.com.
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