Best userscript manager extensions

Tampermonkey is the userscript manager most people start with, and the one most scripts are written and tested against. The Chrome listing shows about 12 million users, and it also runs on Edge, Firefox and, as a paid app, Safari. It installs, updates and switches the small JavaScript programs that run on sites you name.

It has a built-in code editor, per-script settings and a broad set of GM_ functions that scripts use to store data, make requests and add menu items. Scripts can sync between browsers and update automatically. The Chrome version runs on Manifest V3 and uses Chrome's userScripts permission, so since version 5.3 you must switch on the Allow User Scripts toggle (Chrome 138 and later) or Developer mode for it to run anything. Its FAQ covers both.

The trade-off is openness. Tampermonkey was open source until version 2.9 in January 2013 and has been proprietary since, so you rely on the developer's word for what the extension does. Its FAQ says the author has no interest in users' data, and that it needs access to every page because it cannot know where your scripts will run. The scripts you add are the real risk. For most people, it is the easiest place to start.

Violentmonkey is the open source answer to Tampermonkey. The code is public on GitHub under the MIT licence, the extension is free, and it is aimed at the same job: running userscripts on the sites you pick. It works with the common Tampermonkey-style metadata, so most scripts written for other managers install without changes.

It has a built-in editor, script settings, sync providers and automatic updates, and a recent release added a GitHub-compatible server as a sync option and a cron-style schedule for update checks. The Chrome and Edge builds are Manifest V3 and use Chrome's userScripts permission, so you need to switch on the Allow User Scripts toggle (Chrome 138 and later) or Developer mode. The Firefox version still uses Manifest V2, which Firefox continues to support.

The Chrome Web Store listing is now a Manifest V3 build at version 2.50.0, updated on 27 October 2026, after a GitHub request that had been open since October 2023. There is no Safari version, and its site tells Opera users to install from the Chrome Web Store because Opera no longer reviews it. If you want a manager whose code anyone can audit, this is the one we would choose.

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.

Userscripts is a small, open source userscript manager built for Safari. It is a free app from the App Store for iPhone, iPad and Mac, and its source is public on GitHub under GPL-3.0. It runs JavaScript and CSS on the sites you choose, and it keeps your scripts as plain .user.js files in a folder you pick.

That file-based approach is its best idea. On Mac you can edit scripts in the built-in editor, and on any device in a text editor you prefer, and a folder in iCloud can carry them between devices. On iOS you install a script by opening a .user.js link in Safari or by saving the file into the folder. It supports common metadata such as @match, @run-at and @inject-into, with its own set of GM functions.

The developer's privacy policy says it does not collect any data from users. It is not as feature-rich as the Chrome and Firefox managers, and the project documents some quirks, such as iCloud sync delays and needing to open the popup after editing files externally. Tampermonkey also has a paid Safari app, but Userscripts is the free, open one. The latest stable GitHub release is from January 2026. For Safari, it is where we would start.

Greasemonkey is where userscripts started. It is a free, open source manager for Firefox, licensed under MIT, and the other managers took their script format from it. Its Add-ons page describes it as a way to customise how a page displays or behaves using small bits of JavaScript.

It does the core job without a lot around it: install a script, edit it in the built-in editor, turn it on or off, and let it update itself. Recent releases added a @match line for the current page when you start a new script and better messages when automatic updates fail. It supports the GM.xmlHttpRequest function and other standard calls, and because it is Firefox only, there is no Allow User Scripts step to deal with.

Its limits are scope and pace. It runs on Firefox alone, the feature list is shorter than Tampermonkey's or Violentmonkey's, and development is slow, though the GitHub project received a version bump to 4.14 in June 2026. Some modern scripts use features it does not offer. The extension has about 157,000 Firefox users and a 4.2 rating from 1,293 reviews. It is a good, quiet fit if you use Firefox and want something small, but most people will be happier with Violentmonkey or Tampermonkey.