← All extensions

Viewport Tester

Test responsive breakpoints in a real window

chromeedgebraveoperafirefox🔒 Zero telemetryVersion 1.0.0
Download the extension for ChromeDownload the extension for Firefox

Description

Opens the current URL in a real, resized browser window (mobile 375×667, tablet 768×1024, laptop 1366×768 or custom sizes): no iframe faked by CSP or transforms, so media and hover queries stay real. Save your own custom presets. 100% offline, zero telemetry.

Features

  • Ready-made presets: mobile, tablet, laptop and desktop
  • Real resized window: authentic media and hover queries
  • Custom sizes with validation (200–5000 px)
  • Saved, reusable custom presets
  • No iframe: immune to CSP blocks and transform distortion
  • 100% offline, no data leaves the browser

Privacy

100% local processing in your browser. Zero telemetry: no data is sent to external servers.

Required permissions

  • storage

Screenshots

Viewport Tester

Supported browsers

chromeedgebraveoperafirefox