I built a free responsive tester because DevTools only shows one device at a time

DevTools responsive mode has one limitation that's never been fixed: you see one device at a time. You check iPhone. Looks fine. Switch to iPad. Fix padding. Switch back to iPhone. Was the header already broken or did you just break it? I got tired of holding layouts in my head, so I built a tool that shows all three at once. Responsive Tool — free, no signup Paste a URL → phone, tablet, and desktop load at one time. That's it. A few things that make it actually useful day to day: Swap one pane to a different device without losing the other two Refresh one pane after a code push — no need to reload everything Share your exact setup via URL — a teammate sees the same device comparison you do Sync scroll across all panes with a one-line script snippet Every viewport is a real verified CSS size , not a guess No account. No extension. No download. Runs in the browser. I don't see or store the URLs you test. Also: way more sites block iframes via X-Frame-Options than you'd think. I tested ~60 real sites — 93% of developer portfolios loaded fine, but only 44% of framework/marketing sites did. If your site doesn't load, that's the server blocking iframes, not a bug in the tool. Stack Next.js 16 · React 19 · TypeScript · Tailwind v4 · Cloudflare Workers Bonus I also built a CSS breakpoints reference that maps common breakpoints to real device viewports. Handy even without the tool. 👉 responsivetool.com What do you use for responsive checking? Still just DevTools? I want to know what I'm up against.