<meta name="viewport" content="width=device-width,initial-scale=1">

shrink-to-fit is dead

If your users don’t run iOS 9.0–9.2, then you can omit shrink-to-fit=no from your viewport declaration.

However, if you’re looking to get your responsive site on the Apple Watch, then you’ll need <meta name="disabled-adaptations" content="watch">. Thanks Apple!

width=device-width

But of course! Responsive design requires a fluid viewport across all devices.

This also disables the 300-millisecond tap delay on mobile Chrome, Safari, and Firefox. For Edge, you’ll need touch-action: manipulation.

initial-scale=1

This prevents iOS layout shifting on device rotation.

It also prevents mobile browsers with misfiring “mobile-friendly” heuristics from needlessly zooming the page.

shrink-to-fit=no

This section is kept here for historical reasons.

Official Safari 9.1 developer documentation § Viewport changes

Surprise! iOS 9 broke your responsive site because a bunch of sites abused the meta viewport. Why? Depending on what you want to believe…

  1. Scummy sites had <meta name="viewport" content="width=device-width"> to look mobile-friendly on Google, though they definitely weren’t
  2. Compatibility with iOS8 Multitasking, which brought more viewport diversity to sites that weren’t ready for it

Either way, sites had broken viewports, so blah blah blah this is why we need web standards.

In rare form, Apple made a way to disable this, then published it absolutely nowhere. It first appeared in the wild within Apple's developer forums, then confirmed by a WebKit developer.

And that’s that

When do we get CSS @viewport, anyway?