Claude Fable built a browser music app in about 20 minutes

Claude Fable turned a personal music-tool idea into a working browser app in about 20 minutes. The result was SG-16 SIGNAL, a sampler and groovebox inspired by classic SP-1200 and TR-808 music hardware. It ran fully on the client side with HTML, CSS, JavaScript, and the Web Audio API, with no plugins or server dependencies.

The workflow started by asking Claude Opus to create a detailed Fable prompt, including a plan for the Pro account’s 5-hour usage block. The prompt also asked Fable to create a save state, session summary, file path bookmarks, error log, and a Terminal command for saving notes into Obsidian if the one-shot build could not finish. The first build used about 40% of the available usage, and adding missed features like a wav splicer and mixing console used another 40%.

Other Fable 5 examples point in the same direction: it handled WebGL and shader work, checked rendered graphics with screenshots, helped build a reasoning test harness, and automated multilingual app store screenshots through Claude Code, Firebase data, mobile simulators, post-processing, and a repeatable script. The limits are also visible: science-related keywords can trigger safeguards even for simple life-science tasks, and one security check found a real hidden PowerShell startup entry but then had its own warning caught by safety filters.