Parapet is a visual development interface for Rails. It runs beside your app and brings the inner loop into one browser window: test runs with live feedback, file exploring and editing, and CSS layout checks. Its CSS basis is QSS (Quantized Spatial Styling), a layout framework published as its own gem. Parapet's layout behaviour is documented in the QSS gem, not here. Parapet is designed to help you spec, test, and develop faster with AI coding agents in the loop. Each run and change is recorded as performed by a human or an AI agent, so the history shows who did what. Parapet is for development only. It refuses to boot in any environment other than development or test. Work in progress: features are documented as they are implemented.