Responsive Tester

Why I built it

Checking a responsive layout usually means dragging the DevTools window, switching device presets one at a time, or picking up a drawer full of test phones, and the bug still slips through on the one size you skipped. Responsive Tester puts every screen in one Chrome tab and keeps them in sync.

Features

• Phones, tablets and desktops side by side, with 100+ real device frames or your own custom sizes and User-Agent.
• Real-time sync: scroll, click and type once and every screen follows.
• Let AI test every screen: works with Claude, Cursor, Codex, Gemini CLI and Windsurf over MCP. Ask in plain English and get pass / fail per device, with the overflowing elements named.
• Tweak CSS live, Figma-style: click any element to change size, color, spacing or text on one or all screens.
• Inspect elements right inside the testing workspace.
• Screenshots and area capture with annotation (arrows, boxes, highlights, text), stored in a local gallery.
• Tab recording to WebM with built-in compression, for bug reports.
• Isolated sessions for logged-out or fresh-session testing.

Free on the Chrome Web Store. Recording and screenshots are processed locally in the browser.