The ultimate responsive web simulator and AI-powered QA suite running directly inside Google Chrome. Mirror scrolls, clicks, and form inputs simultaneously across Mobile, Tablet, and Desktop in 60/120 FPS. Capture full-page bug evidence, compress videos in-browser, and automate testing with AI.
Explore high-resolution captures of Responsive Tester in action across real development workflows.
Side-by-side viewport preview with synchronized scroll, click ripples, form mirroring, and one-click portrait/landscape orientation.
Hover and inspect computed styles, media query breakpoint triggers, and catch frame-level JavaScript console warnings directly.
Stitch entire scrollable web pages with zero seams. Annotate with arrows and step badges. Record high-def WebM videos and compress files locally using Offscreen Web Workers.
Connect Claude, Cursor, Antigravity, or ChatGPT to run responsive audits, verify form validation flows, and detect UI overlap bugs automatically.
Eliminate device-switching friction, capture ironclad visual bug evidence, and automate regression audits with AI.
Interact on any single device viewport and watch all others mirror your actions with 60/120 FPS precision.
True presentation fidelity simulating iOS 15β18 Safari bottom address bar collapsing on scroll, Dynamic Island, and laptop display bezels.
Test mobile-only redirects, adaptive SSR logic, and search crawler rendering without modifying test code or DNS.
navigator.userAgentData and mobile hints
Never experience blank screens or "refused to connect" errors. Built-in Declarative Net Request rules bypass iframe restrictions.
frame-ancestors policy lifted strictly on test tabs
Capture indisputable visual evidence in seconds with in-browser video compression for instant attachments on GitHub, Jira, and Slack.
Highlight bugs and communicate design defects with clarity using the integrated canvas drawing suite.
Measure element dimensions, spacing, typography, and breakpoint triggers, or test guest flows in fresh sessions.
Zero data collection. All simulations, screenshot captures, and recordings run 100% client-side inside your browser.
See how Responsive Tester combines browser-native performance with the features of heavy desktop apps.
| Feature Capability | π± Responsive Tester (ScreenSync) | π₯οΈ Responsively App | π οΈ Chrome DevTools Device Mode |
|---|---|---|---|
| Multi-Screen Simultaneous View | β Side-by-side in single Chrome tab | β Side-by-side in Electron window | β Single viewport toggle only |
| Real-Time Scroll & Click Sync | β 60/120 FPS + Visual ripples | β οΈ Basic synchronization | β Manual interaction per screen |
| Memory Footprint & Installation | β Zero install (lightweight MV3 extension) | β Heavy 1.2 GB+ standalone Electron app | β Built into Chrome |
| Collapsible Safari Bottom Chrome | β Realistic iOS 15-18 Safari dynamic bar | β Static frame without Safari collapse | β Generic viewport cutouts only |
| Localhost & CSP Frame Bypass | β Built-in DNR rules (no blank screens) | β οΈ Requires manual proxy settings | β Native origin access |
| Full-Page Screenshot Stitching | β Zero-seam scroll & stitch | β οΈ Often clips sticky headers | β οΈ Clunky DevTools command menu |
| Silent Video Recording & Compression | β Built-in in-browser WebM compressor | β Requires 3rd-party screen recorder | β No video recording capability |
| Autonomous AI MCP Integration | β 12 tools for Claude, Cursor, Antigravity | β No Model Context Protocol support | β No native MCP bridge |
| Price & Licensing | β 100% Free Forever (Open Source MIT) | β Open Source | β Free |
ScreenSync natively connects with Claude Desktop, Cursor, Antigravity, and ChatGPT through the lightweight responsive-tester-mcp package (identifier: rstest). Run layout audits, inspect visual bugs, and harvest console errors using natural language.
localhost:3000.
{
"mcpServers": {
"rstest": {
"command": "npx",
"args": ["-y", "responsive-tester-mcp@latest"]
}
}
}rstest)
Click any card below to copy the prompt directly to your clipboard:
| Canonical Name | rstest Alias |
Parameters | Description |
|---|---|---|---|
| responsive_navigate | rstest_navigate |
url (string, req) |
Loads target URL into all active device viewports. |
| responsive_capture_screenshots | rstest_capture_screenshots |
deviceId (optional) |
Captures high-res base64 PNG snapshots for LLM visual review. |
| responsive_open_viewer | rstest_open_viewer |
url, reload |
Auto-launches and focuses Responsive Tester in Chrome. |
| responsive_interact | rstest_interact |
action, selector, value |
Simulates clicks, form inputs, and synchronized scrolling. |
| responsive_set_user_agent | rstest_set_user_agent |
mode, rewriteNetworkHeaders |
Sets UA emulation profile (iOS Safari, Android, Googlebot, etc.). |
| responsive_get_logs | rstest_get_logs |
None | Collects runtime JavaScript exceptions and console errors. |
Install directly from the Chrome Web Store or load unpacked for development.
Open the official Responsive Tester listing on the Google Chrome Web Store.
Confirm permissions. Responsive Tester operates 100% locally and never transmits your browsing data.
Pin Responsive Tester to your toolbar. Click the icon anytime on any webpage to open the studio.
Clone the repository from GitHub or download the source release zip.
Navigate to chrome://extensions/ in Chrome and toggle Developer mode ON.
Select the root directory containing manifest.json. The extension will activate instantly.
Configure your AI client with npx -y responsive-tester-mcp@latest or use the 1-Click prompt above.
Launch Chrome and open Responsive Tester. The status badge will turn β AI Online (ws://127.0.0.1:8765).
Ask Claude or Cursor: "rstest: audit localhost:3000 across mobile and tablet viewports."
Common queries regarding multi-screen synchronization, localhost security, and AI integrations.
http://localhost:3000, http://localhost:5173, http://127.0.0.1:8080, and corporate intranet IP addresses. Because all testing runs locally inside your browser, no tunneling (like ngrok) is required.
declarativeNetRequest API (Manifest V3) to selectively strip X-Frame-Options (DENY, SAMEORIGIN) and Content-Security-Policy: frame-ancestors headers strictly on simulation tabs. This ensures websites embed smoothly without blank screen errors.
responsive-tester-mcp package creates a local WebSocket bridge (ws://127.0.0.1:8765) to your Chrome Extension. Simply ask your AI with rstest to navigate, click, take screenshots, and detect layout issues automatically.