What Is Responsive Breakpoint Previewer?
Responsive Breakpoint Previewer shows how a piece of HTML and CSS renders at different screen widths, from a 320px phone to a 1440px desktop. Paste your markup, step through standard breakpoints or drag to any width, and catch layout issues before they reach production.
How to Use This Tool
Click Edit HTML and paste your markup with its styles, then pick a preset width (Mobile S 320px through Wide 1440px) or drag the slider anywhere from 280 to 1600px. The preview is a sandboxed frame at exactly that width, so your media queries respond as they would on a device of that width; on a smaller screen the frame is scaled down to fit. Everything runs in your browser.
Why Use Responsive Breakpoint Previewer?
Chrome DevTools responsive mode only shows one size at a time. This tool lets you view multiple breakpoints simultaneously, making it faster to spot layout breaks, text overflow, and alignment issues across the full range of screen sizes. It’s free, instant, and requires no browser extensions. For a detailed walkthrough, see our step-by-step guide.
Common Use Cases
Sanity-checking a layout at the breakpoints your stylesheet actually targets, instead of guessing what 768px or 1024px will look like by dragging a window. Walking a client through a component at each width, one click per breakpoint. Catching the typical mid-breakpoint failure modes — a heading that breaks awkwardly at 900px, a navigation that collapses too early on tablets, an image that loses focal-point cropping at landscape phone widths.
Checking a component at phone, tablet and desktop widths without resizing the browser window. Spotting regressions after a CSS change: paste the updated markup and step through the breakpoints. The tool is also useful for content reviews, where non-designers can see at a glance which breakpoints a piece of copy survives and which break it.
How We Compare
Chrome DevTools device mode is the gold standard for one-viewport inspection and ships with realistic device presets, touch emulation, and throttling. The limitation is that it shows one device at a time, so cross-breakpoint comparison means tabbing between presets. Polypane and Sizzy are paid multi-viewport browsers that solve exactly that problem and add scroll/click sync, but they're desktop apps with subscription pricing.
This tool sits between them: open it in any browser, paste a component's HTML and CSS, and step through common breakpoints with real media-query behaviour, no install, no account. Pair it with our container query builder when you're converting component-level responsive rules off the media-query layer.
A practical pointer: the previewer takes HTML and CSS you paste, not a live URL. To check a deployed page, open it in your browser's DevTools device mode, or paste the relevant markup and stylesheet here.
Frequently Asked Questions
Built by Derek Giordano · Part of Ultimate Design Tools