Tab Spoofer

A lightweight Chrome extension that prevents websites from detecting tab switches.

Websites detect tab switches through a handful of browser APIs — Page Visibility, focus/blur events, document.hasFocus(), and more. Tab Spoofer intercepts all of them at the earliest injection point (document_start) so the page always believes you're present and focused.

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How it works

Method	What sites use it for	Spoof
document.visibilityState	Check if tab is active	Always returns "visible"
document.hidden	Boolean visibility flag	Always returns false
visibilitychange event	React to tab switch	Blocked before site handlers run
window blur	Detect loss of window focus	Stopped at capture phase
document mouseleave	Detect cursor leaving browser	Stopped at capture phase
focusout	Detect when no element is focused	Stopped at capture phase
document.hasFocus()	Polled focus check	Always returns true

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Install

1. Clone or download this repo
2. Open Chrome and navigate to chrome://extensions/
3. Enable Developer Mode (toggle, top right)
4. Click Load unpacked and select the tab-spoofer/ folder

The extension is now active on all pages. No restart required.

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Test it

Open index.html or go to Tab Spoofer — Test Page in Chrome after loading the extension. Switch tabs — all counters should stay at zero. Click Run manual checks to verify the spoofed property values directly.

Without the extension, switching tabs immediately triggers the red indicators.

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Targeting a specific site

By default the extension runs on all URLs. To limit it to one domain, edit manifest.json:

"matches": ["*://example.com/*"]

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Limitations

This extension only bypasses JavaScript-based detection. The following are out of scope:

• Server-side timing — gaps in API calls or heartbeats are visible server-side; no client spoofing can hide them
• requestAnimationFrame pause detection — rAF stops in background tabs; apps that track frame timing will notice
• setInterval drift — background tabs throttle timers; some apps detect the drift

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Files

tab-spoofer/
├── manifest.json   # Manifest V3 extension config
├── spoof.js        # Injection script — runs before page JS
└── index.html      # Standalone test page

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License

This project is licensed under the MIT License.

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Made with ❤️ by Arman Singh