Log In Sign Up Free

📱 Responsive Design Checker

Paste any URL and see it rendered at iPhone, iPad, MacBook, 1440p and 4K viewport sizes — side by side. Live iframes, no server round-trip.

Try: toolspow.com wikipedia.org css-tricks.com tailwindcss.com web.dev
⚠ Some sites block iframe embedding (X-Frame-Options / CSP). Google, Facebook, Twitter, Stripe, GitHub and many banking / SaaS sites will show a "site blocks embedding" message. Sites without that header (documentation, blogs, marketing pages) load fine.
Zoom 40%
👀

Paste a URL to preview

Try one of the sample sites above.

Ready

About Responsive Design Checker

Responsive Design Checker lets you preview any website at multiple device sizes at once — from a 375 px iPhone SE all the way up to a 3840 px 4K monitor. Instead of resizing your browser window over and over, drop a URL and see how the page behaves on eleven common device viewports simultaneously. Grid layout shows them all side by side, or switch to Single mode to focus on one device with more room to scroll.

Everything runs client-side using standard <iframe> embeds. Nothing about the target URL touches our server — your browser fetches the target directly.

Iframe limitation: some websites send X-Frame-Options: DENY or CSP frame-ancestors that forbid embedding. Those sites will render a "blocks embedding" message with a click-through to open in a new tab. This is a browser policy, not a bug in the tool — Chrome DevTools' device toolbar avoids it because it's inspecting your own tab.

How to use

1

Paste a URL

Bare domain works too — we add https:// automatically.

2

Choose devices

Toggle chips for the viewports you care about. Default set: iPhone SE, iPhone 15 Pro, iPad Mini, MacBook, Desktop 1440p.

3

Compare

Grid mode fits all viewports on screen with a zoom slider. Single mode focuses on one at 100% scale.

4

Iterate

Change the URL, click Reload all, add a custom width, rotate any device — everything's fast and local.

Key Features

11 device presets

iPhone SE (375×667) · iPhone 15 (390×844) · iPhone 15 Pro Max (430×932) · Pixel 8 (412×915) · Galaxy S24 (360×780) · iPad Mini (768×1024) · iPad Pro (1024×1366) · MacBook 13 (1280×832) · MacBook Pro 16 (1728×1117) · Desktop 1440p (1440×900) · Full HD (1920×1080) · 4K (2560×1440).

Custom viewport

Enter any width × height in pixels. Perfect for testing edge-case widths (280 px old phones, 320 px iPhone SE 1st gen, 1366 px legacy laptops).

Rotate per device

Click the ↻ button on any device header to swap width and height — quick way to check landscape orientation without dragging sliders.

Sync scrolling

Enable "Sync scroll" and scrolling one frame scrolls the others proportionally. Great for spot-checking that your responsive design lines up at every breakpoint.

Zoom slider

Scale the grid from 30% to 150% to fit more devices on your screen or zoom in for a closer look. Handy on a laptop when you want to see mobile and desktop simultaneously.

Layout toggle

Grid — all selected viewports visible at once. Single — one device at a time, full size, more scroll room. Use single mode for detailed pixel-hunting.

Reload all

One button reloads every iframe simultaneously — great for testing after a deploy or CSS change on your dev site.

Share URL

The current URL is encoded in the address bar — copy it to send someone the exact same preview setup.

Common Use Cases

  • Sanity-check a marketing page after a CMS content edit
  • Compare mobile vs desktop layout of a hero section
  • Test how a blog post renders on 4K without owning a 4K monitor
  • Spot media-query breakpoints that aren't kicking in properly
  • Quickly demo a design to a client on multiple devices at once
  • Verify that new landing pages don't overflow on old phones
  • Show developers where a menu breaks at tablet width
  • Preview competitor sites at every viewport for research
  • QA visual regressions after a Tailwind / Bootstrap version bump

Security & Privacy

  • 100% client-side: the URL you enter loads directly in your browser via iframe. Our server never sees the URL or fetches it.
  • Works offline for cached sites: once the target has loaded once in a session, browser cache serves it fast.
  • Third-party cookies still apply: logged-in state on the target site persists inside the iframe. If you're logged into your own dev site, the iframe shows the logged-in view — that's usually what you want.
  • No signup, no logging.

Frequently Asked Questions

The target site sends a header (X-Frame-Options: DENY or Content-Security-Policy: frame-ancestors 'none') that instructs your browser to refuse embedding. It's a clickjacking protection. Google, Facebook, banking, and most SaaS use it. There's no way for a client-side tool to bypass this — it's the browser enforcing the header from the target.
Most documentation sites, blogs, marketing pages, small-business sites, personal portfolios, and CMS-default installs will embed fine. Sites that block: Google properties, Facebook, Twitter/X, GitHub, Stripe, most banks, and SaaS apps that log you in. Try your target — if it fails, you'll see a friendly message with a "Open in new tab" link.
No — the zoom slider only scales the visual size of each iframe on your screen via CSS transform. The iframe still renders internally at its true pixel dimensions (e.g. 375×667 for iPhone SE). Media queries fire at the true dimensions, not the scaled ones.
Some sites decide to serve a mobile layout based on the User-Agent header (not viewport width). Browsers don't let iframes spoof their UA — they always use the parent tab's UA. This is a limitation of the iframe approach; Chrome DevTools' device toolbar can spoof UA because it's inspecting your own tab. For true UA-based sites, use DevTools or a headless-render service.
No. Everything runs client-side. The iframe loads the target directly from your browser — our server never fetches it. Verify with DevTools → Network.
Yes — no signup, no ads, no limits.