Tampermonkey

Tampermonkey is a cross-browser extension and userscript manager that enables the execution of custom JavaScript on web pages. It is designed to extend or modify the behavior and appearance of websites by running small scripts created by users.

It runs on major browsers such as Google Chrome, Microsoft Edge (Chromium-based), Mozilla Firefox, Safari, and Opera. It serves as an alternative to Greasemonkey, offering a rich user interface and script management features. Scripts can be installed from the Tampermonkey gallery or from direct URLs, and can be edited in an integrated editor. Each script can specify metadata including @name, @description, @match, and @grant to control which pages it runs on and what permissions it requests.

Tampermonkey provides a dashboard to enable, disable, and organize scripts; automatic updates; per-script and global options; and a synchronization service that can sync scripts across devices with a user account. It also provides a developer API that mimics Greasemonkey's GM_* functions for storage, network requests, and resources, with run-at options like document-start and document-idle.

As with other user script managers, Tampermonkey runs code within the context of the web page and can access page content and user data. This capability introduces security risks if scripts are obtained from untrusted sources; users should review scripts and use trusted repositories. The project is maintained to support a broad ecosystem of scripts that customize web browsing experiences.