About ScriptCat
ScriptCat takes Tampermonkey's design and adds to it. It is an open source manager licensed under GPL-3.0 that runs ordinary userscripts, and it also runs background and scheduled scripts that keep working without a page open. Its README describes full compatibility with Tampermonkey scripts, so migrating means copying your scripts across.
The extras are practical: scheduled tasks for things like automatic check-ins or reminders, cloud sync, subscriptions that bundle scripts into collections, and a built-in editor with completion and syntax checking. The Chrome build is Manifest V3 (version 1.5.0 at the time of writing) and uses the userScripts permission, so you need the Allow User Scripts toggle on Chrome 138 and later. It is also listed for Edge and Firefox, but the Firefox listing is an older 0.16 build.
It is the least established of the managers here. The Chrome listing shows about 100,000 users, against 12 million for Tampermonkey. The project is active, with a release in October 2026. Background scripts are powerful, so give them the same scrutiny you would give any code that runs unattended. Choose it if you want automation that Tampermonkey does not offer.
Pros and cons
- Open source under GPL-3.0
- Background and scheduled scripts, not only page scripts
- Compatible with Tampermonkey scripts
- Cloud sync, script subscriptions and a built-in editor
- Smaller Chrome user base than Tampermonkey or Violentmonkey
- Only about 74 ratings on the Chrome store, so less track record
- No Safari version
Permissions
It requests access to all websites, plus the userScripts, scripting and web request permissions that userscripts and their GM functions need. Downloads, cookies and notifications support what scripts can do on your behalf.
