Viewport extension
Install
Radial Viewport is a free Chrome extension for responsive testing: the breakpoint UX from the Radial app, on its own. It loads the current page inside a resizable frame, so the site's real responsive CSS actually fires. It's standalone: not connected to the Radial app in any way, and it collects nothing (see the Viewport privacy policy).
Want to try before installing? The Viewport page runs the actual extension UI in your browser. Everything works there except screenshots, which need the installed extension.
From the Chrome Web Store
Add Radial Viewport from the Chrome Web Store, then pin it. On any page, click its icon and the page opens in a resizable viewport tab.
Install unpacked
Running a pre-release tester build instead? It installs unpacked:
- Unzip the build somewhere it can stay (Chrome loads the extension from that folder, so don't delete it afterward).
- Open
chrome://extensions. - Toggle Developer mode (top right).
- Click Load unpacked and select the unzipped folder, then pin it.
How it frames arbitrary sites
Many sites send X-Frame-Options or CSP
frame-ancestors headers that block being shown in an
iframe. Viewport strips those response headers
only inside its own viewport tabs. The rules are
session-scoped and keyed to the tab id, so every other tab keeps its
protections intact. A few sites with JavaScript frame-busting may
still refuse to load; that's the one limitation of the iframe
approach.
What the permissions are for
| Permission | Used for |
|---|---|
tabs, webNavigation |
Opening the viewport tab and keeping the address bar in sync as you navigate. |
declarativeNetRequest, <all_urls> |
The per-tab header rules above, so any site can load in the frame. |
scripting |
Injecting the inspect, edit, and comment overlays into the framed site. |
storage |
Persisting your comments and text edits per site, locally. |
Nothing leaves your machine. The extension has no server and no analytics.