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scriptscat/scriptcat

A browser extension that runs userscripts, fully compatible with Tampermonkey scripts and adding background and scheduled script execution.

Open-source alternative to:Tampermonkey

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What is it?

ScriptCat is a userscript manager for Chrome, Edge and Firefox. It lets you customize web pages, remove ads and automate repetitive browser tasks by installing scripts that run on matching pages.

The extension aims for full compatibility with Tampermonkey scripts, so existing scripts can be installed directly. Beyond page-bound scripts, it adds a background script mechanism that keeps scripts running independently of any open page, along with scheduled scripts for timed tasks such as auto check-ins or reminders.

Scripts run in isolated sandboxes and must request permissions explicitly, with extra confirmation for sensitive operations. A built-in editor provides syntax highlighting, completion and ESLint, and cloud sync keeps scripts consistent across devices.

Key features

  • 01Compatible with most Tampermonkey userscripts.
  • 02Background scripts that run without depending on an open page.
  • 03Scheduled scripts for timed tasks.
  • 04Sandboxed execution with explicit permission requests.
  • 05Built-in code editor with syntax checking and ESLint.
  • 06Script cloud sync and script subscriptions.

Use cases

  • Removing ads or restyling websites with custom scripts.
  • Automating daily check-ins or repetitive web actions.
  • Migrating existing Tampermonkey scripts to another browser setup.
  • Developing and debugging userscripts with a built-in editor.

Quick start

  1. 1

    Install the extension from the Chrome Web Store (Stable Version)

  2. 2

    Install the extension from the Edge or Firefox store, or download the ZIP from GitHub Releases for manual installation

  3. 3

    Install scripts from ScriptCat Script Store or other userscript markets

Things to know

  • Distributed as a browser extension, so it only runs in supported browsers.
  • Firefox version is MV2, and the README gives no further detail on its limitations.

Topics

#userscript#browser-extension#tampermonkey#chrome-extension#automation#web-customization#greasemonkey-userscript#scriptcat#webextension

FAQ

What is scriptcat?
A browser extension that runs userscripts, fully compatible with Tampermonkey scripts and adding background and scheduled script execution. ScriptCat is a userscript manager for Chrome, Edge and Firefox. It lets you customize web pages, remove ads and automate repetitive browser tasks by installing scripts that run on matching pages.
Is scriptcat free to use? What license does it have?
scriptcat is open source under the GPL-3.0 license. Check the license terms before using it in commercial products.
Is scriptcat still maintained?
Actively maintained. The last commit to scriptcat was on Oct 21, 2026.
What can I use scriptcat for?
Removing ads or restyling websites with custom scripts. Automating daily check-ins or repetitive web actions. Migrating existing Tampermonkey scripts to another browser setup. Developing and debugging userscripts with a built-in editor.
How do I install scriptcat?
Install the extension from the Chrome Web Store (Stable Version) Install the extension from the Edge or Firefox store, or download the ZIP from GitHub Releases for manual installation Install scripts from ScriptCat Script Store or other userscript markets
Where can I get scriptcat?
The source code and installation instructions are on GitHub: https://github.com/scriptscat/scriptcat

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