Responsive Preview

How to use it

1. Pick a preview mode: external URL or pasted HTML.
2. In URL mode, type the address and press Load preview — nothing loads until you do.
3. In HTML mode, paste markup into the panel; every frame updates as you type.
4. Read the four frames side by side: 375, 768, 1024 and 1440 pixels wide, each labeled.
5. In HTML mode you can switch on sync scrolling so all frames move together.

Common use cases

• Checking a breakpoint fix — see the phone, tablet and desktop layouts in one screen.
• Quick responsive sanity check — load a page and look for horizontal overflow at 375px.
• Previewing a fragment before saving it — paste a snippet and judge the layout without creating a file.
• Comparing widths while you edit CSS — paste the HTML once and keep the frames open next to your editor.

Why it stays private

This tool itself makes no network request and stores nothing. In URL mode the request is made by your own browser directly to the site — there is no proxy, no cache and no logging in between. Pasted HTML renders in a sandboxed iframe without script permission, so the markup cannot run code.

FAQ

Q: Why does the page not load in URL mode? A: Many sites send X-Frame-Options or a Content-Security-Policy that forbids framing. That is the site's decision and this tool cannot override it — open the page in a tab instead.

Q: Is my URL sent anywhere? A: No. The address is only written into the iframes on this page, and your browser fetches the site directly. Nothing is proxied through a server.

Q: Why is scroll sync disabled for URLs? A: Cross-origin frames do not expose their scroll position, for obvious security reasons. Sync therefore works only in HTML mode, where the frames are same-origin.

Q: Does pasted HTML run scripts? A: No. The sandbox grants no script permission, so script tags, event handlers and external requests from the markup are all blocked.