Notice
This page show a previous version of the articleA bookmarklet is a relatively short piece of JavaScript code (of perhaps 100 to 2000 characters in length) that the browser runs on the current page. It begins with "javascript:" instead of "http://". Otherwise, you can treat it just like any standard bookmark. For instance, in Firefox, you can keep a bookmarklet together with your other bookmarks on the bookmark bar.
Whereas a user script is typically installed from a site such as http://userscripts.org, bookmarklets can be saved by whichever means you use to create a bookmark. Simply replace the "Location" or "URL" field by the bookmarklet string.
Tatoeba bookmarklets
See also
See the Wikipedia page on bookmarklets or this short introduction for more details on bookmarklets.