Embervale, a browser RPG with no asset files that playtests itself

The full story

Embervale is a small-party action RPG in which you lead three heroes through an isometric valley. Act I has five story quests, six side quests and four bosses, and unlocks a ten-floor dungeon, about two hours of play in all. It is plain HTML, CSS and JavaScript with no build step; every sprite and spell effect is drawn with canvas code and every sound is synthesised with Web Audio, so there isn't a single image or audio file.

Opus 5.5 built it in the Claude app over roughly two days and 60 to 70 prompts, working in its own cloud workspace with a shell, Node and a headless browser. One prompt often set off a long run: build, run the playtest bot, screenshot every zone, compare frame times and hand back a zip. The poster found a "change queue", batching their notes before asking for them to be built, caused much less drift than one-off requests.