Viewport

The viewport is the visible area of a web page inside the browser window. On mobile devices, pages control how they scale to the screen with a <meta name="viewport"> tag, which sets the page width and zoom behavior - including, undesirably, the ability to prevent users from zooming.

Without this tag, mobile browsers default to rendering the page at a fixed desktop-like width (typically 980px) and shrinking the result to fit the screen, which is illegible until the visitor zooms in manually. Declaring width=device-width is what makes responsive design and its media queries actually take effect on mobile.

Learn more

• Viewport concepts - MDN's explanation of the viewport and the viewport meta tag
• Responsive design