Building PLANET GUARD: A Full Game, Built by Talking to an Agent

This one is a video, recorded from the actual development session rather than staged after the fact — including a couple of terminal and code-editor scenes recreated from the real commands and real diffs that happened, so the pacing is watchable without hunting through raw screen-capture noise.

(Narration is in Chinese; the code and commands on screen are in English and should be readable either way.)

What it’s actually showing

PLANET GUARD is a small browser bullet-heaven built for Play Grid, our free mini-games arcade. The premise inverts the usual survivor-game formula: instead of moving a character to dodge danger, the planet sits fixed at the center of the screen and never moves at all. The only input is a drag that spins a defense ring around it — weapons fire automatically once equipped, and the entire skill ceiling comes down to deciding which direction gets covered.

The video walks through:

The origin — a five-second clip from an unrelated hyper-casual ad was the entire creative brief. No gameplay footage worth copying, just a feeling (“a planet ringed by light, meteors closing in”) that had to get written down as an actual design document before any code existed.
AI-generated art — concept sheets for the planet, six enemy types, and a weapon-icon set, all sharing one style prompt so they’d read as one game instead of several. The cover art was generated directly through the MiniMax API — the video shows the real command and its real output.
The core mechanic in code — the entire “rotate instead of move” interaction is about six lines of JavaScript. Seeing it on screen next to the gameplay makes it obvious how small the actual idea was.
Three real rounds of rework — the first shipped version had three weapon systems and ran out of meaningful choices by around level nine. That single piece of feedback became the next full iteration: five tiers per weapon instead of three, two new weapon systems, stackable passive upgrades, and a wave/boss structure with a persistent currency that carries power between runs.

Why bother recreating the terminal instead of just screen-recording it

Browser automation can only capture what happens inside the browser tab it controls — it has no way to record a real terminal or a real code editor running elsewhere on the machine. Rather than skip that part of the story, those two scenes get rebuilt as short animated mockups: a typewriter effect typing out a command, a code editor revealing a diff line by line. The rule that made this feel honest rather than staged: only real commands that were actually run, and real code that was actually written, go into those scenes. The animation is a recreation for pacing. The content isn’t invented.

If you want the deeper version

The full design-and-implementation writeup — with the actual weapon-tier tables, the wave-difficulty curve, and the two “only visible once you actually look” bugs that got fixed along the way (a CSS grid column that silently zeroed out on mobile, and a warning banner that had never once displayed since it shipped) — is on the Play Grid dev blog: Building PLANET GUARD: A Planet That Never Moves.

You can also just play it — it’s free, no install, no account required.