All tools
Responsive viewport planning

Viewport Checker

Use this reference to choose viewport ranges for responsive QA, then open Sizzy to test the same page across real device sizes at once.

viewport width320px - 1199px
Small phones320-389px
Modern phones390-479px
Large phones and small tablets480-767px
Tablet and desktop handoff768-1199px
320-389px

Small phones

Stress-test dense controls, text wrapping, dialogs, and fixed-position UI.

390-479px

Modern phones

Check the default mobile experience and any card, nav, or form density changes.

480-767px

Large phones and small tablets

Watch for awkward intermediate layouts before tablet styles take over.

768-1199px

Tablet and desktop handoff

Confirm columns, sidebars, and nav transformations happen cleanly.

Responsive QA checklist

Start with the narrowest supported mobile width and expand until the layout breaks.

Check common device-width clusters instead of testing only arbitrary breakpoints.

Validate navigation, sticky elements, forms, dialogs, and horizontal overflow at each range.

Repeat the pass with realistic content lengths, logged-in states, and browser chrome assumptions.