URL to Breakpoint Preview
URL to Breakpoint Preview — test any website at mobile, tablet, and desktop sizes instantly. Responsive design testing without resizing your browser. Free.
About URL to Breakpoint Preview
The URL to Breakpoint Preview lets you test how any website renders at different screen sizes — mobile, tablet, desktop, and wide — without resizing your browser window or digging into DevTools. Enter a URL, pick a breakpoint, and see a live preview of the site at that exact viewport width, scaled to fit your current screen.
Responsive design testing is a constant part of modern web development. Every layout decision that works at 1440px desktop width needs to be validated at 768px tablet and 375px mobile. Doing this by manually dragging your browser window to different widths is imprecise and time-consuming. Browser DevTools offer a device emulation mode, but it requires several clicks to activate and does not let you quickly switch between sizes without re-entering them. This tool makes the whole process faster: paste a URL and click a size.
The tool is most powerful for local development servers. Because localhost does not have security headers that block iframe embedding, local sites load cleanly and you can see your layout at any breakpoint as you code. Staging environments that have not added iframe restrictions also work perfectly — making this a useful QA tool before a site goes live.
Production websites from large companies often block iframe embedding as a security measure. If you see a blank preview on a public URL, it is because the site has set X-Frame-Options: SAMEORIGIN or a restrictive Content-Security-Policy. This is not a tool limitation — it is the target site refusing to be framed, which is standard security practice.
The supported breakpoints — 375px (mobile), 768px (tablet), 1280px (desktop), and 1440px (wide) — match the most widely used responsive design reference sizes. These align with common Tailwind CSS, Bootstrap, and custom CSS breakpoint conventions.
Free, instant, no signup, and available in any browser.
Frequently asked questions
Most production websites block iframe embedding using X-Frame-Options or Content-Security-Policy headers. This tool works best with localhost dev servers, staging URLs, or any site that allows iframe embedding.
Mobile (375px), Tablet (768px), Desktop (1280px), and Wide (1440px) — the four most common breakpoints used in responsive web design.
Yes. Local dev servers like http://localhost:3000 do not have iframe restrictions, so they load perfectly in the preview. This makes the tool ideal for checking responsive layouts during development.
A breakpoint is a specific viewport width at which a website's layout changes to accommodate different screen sizes. Common breakpoints are around 375px (mobile), 768px (tablet), and 1280px (desktop).