CSS grid generator

The preview is your browser's own grid engine fed the exact emitted values, so what you see is what ships. Validation refuses what a browser would silently drop: template-areas rows with different cell counts, an area that never forms a rectangle, and names that are not usable identifiers. Warnings call out anything the browser resolves on its own: implicit tracks when areas outnumber declared columns, and the fact that auto-fit and auto-fill decide their count at render time. Nothing about your layout leaves the tab.