Tampermonkey

Tampermonkey is a userscript manager. It lets you add small JavaScript programs that change how a website looks or works in your browser.

Userscripts are small scripts that run on the pages you choose. You can use them to add a button, change a layout or fill in a form. Tampermonkey gives you one place to create, enable, disable and update these scripts. It also makes it simple to install scripts that other people have shared, so you can reuse their work without writing everything yourself.

• Manage userscripts from the browser toolbar popup
• Enable or disable scripts without leaving the page
• Check installed scripts for updates
• Install scripts shared by other users
• Works in several major browsers

Web developers who want to test changes on live sites, and people who want to tweak the websites they use often. It suits anyone who is comfortable reading or writing small scripts.

The extension is free to install from browser stores. The source code is published on GitHub under the GPL-3.0 licence. Scripts run with the permissions you give them, so review any script before you install it, especially one that asks for access to your data.