Why it's a strong pick

ScriptCat is free and open source under GPL-3.0, and the official site says it has no ads. It is Tampermonkey-compatible and adds background and scheduled scripts, which many managers do not offer. The Chrome Web Store listing shows version 1.4.0, updated 9 July 2026. The trade-off: its permission list is long.

What it does

ScriptCat is a userscript manager. It installs and runs scripts that change websites, like other managers. It also runs background scripts that keep working and scheduled scripts that run at set times. The official site calls it an "open-source userscript engine" that is Tampermonkey-compatible. It can move your scripts over from other userscript managers.

Key features

Background scripts. Scripts that keep running without a page open.
Scheduled scripts. Scripts that run at times you set.
Cloud sync and subscriptions. Sync scripts, and follow script collections.
Migration. Bring scripts over from other userscript managers.
Editor. An editor with API auto-completion and ESLint checking.
Script store. One-click installs, per the listing.

Who it's for

ScriptCat suits script authors who need background or scheduled scripts, and people moving from Tampermonkey who want a compatible manager that is open source. If you only need simple page tweaks, Tampermonkey or Violentmonkey may be simpler.

How do I get ScriptCat scripts to run in Chrome?

Turn on "Allow User Scripts" for ScriptCat in Chrome's extension settings if your browser is version 138 or newer. On older versions, enable Developer Mode. The docs add that if scripts still do not run, disable and re-enable the extension, or restart the browser.

Is ScriptCat open source?

Yes. The code is on GitHub, and the repository's licence file is the GNU General Public License version 3. The official site describes ScriptCat as "completely free & open source". It does not name the licence itself, so the GPL-3.0 detail comes from the repository. The manifest is Manifest V3.

What permissions does ScriptCat ask for?

The project's current manifest lists tabs, alarms, storage, cookies, offscreen, scripting, downloads, activeTab, webRequest, userScripts, contextMenus, webNavigation, notifications, clipboardWrite, unlimitedStorage, declarativeNetRequest and debugger, plus access to all sites. This is a long list that includes debugger. The repository is newer than the store version, so check the install prompt.

What does ScriptCat do with my data?

On the Chrome Web Store, the developer states it will not collect or use your data. Its privacy policy is on docs.scriptcat.org. That is the developer's own statement, not an audit. Read the policy before you install, and read each script's permission prompt.

FAQ

Is ScriptCat free? Yes. The official site says "completely free & open source" and "No ads".

Do I need an account? The developer does not say that an account is required. Cloud sync is optional.

Is it Manifest V3? Yes. The project's manifest sets Manifest V3.

Good to know

The permission list is long, and it includes debugger and all-sites access. Install only scripts you trust. ScriptCat's sandbox asks for your consent when a script wants a permission, so read each prompt instead of clicking through it.

Other userscript managers to compare

ScriptCat is one of 3 picks in our userscript managers guide:

Tampermonkey: free, built-in editor, many sync options. Source licence not stated.
Violentmonkey: open source (MIT). No price shown by the developer.

Related: developer tools.

ScriptCat