Paste any URL. See it rendered across all six common Mac display sizes — MacBook Air 13 and 15, MacBook Pro 14 and 16, iMac 24, and Studio Display 5K — stacked, scaled, and labeled. The notch and menu bar are where Apple puts them, so what you see matches a real fullscreen browser. Single HTML file. No signup, no tracking, no build step. Works with localhost. Download once and it runs offline forever.