A bookmarklet is an applet, a small computer application, stored as the URL of a bookmark in a web browser or as a hyperlink on a web page.

Whether bookmarklet utilities are stored as bookmarks or hyperlinks, they are designed to add one-click functionality to a browser or web page. When clicked, a bookmarklet performs some function, one of a wide variety such as a search query or data extraction. Usually the applet is a JavaScript program.

The term is a portmanteau of the terms bookmark and applet.

Concept

Web browsers use URIs for the href attribute of the tag and for bookmarks. The first part of the URI, such as http:, file:, or ftp:, specifies the protocol and required form for the rest of the string. Browsers also implement a prefix javascript: that to a parser is just like any other URI. Internally, the browser sees that the protocol is javascript, treats the rest of the string as javascript code which is then executed, and uses the resulting string as the new page.

The executing script has access to the current page, which it may inspect and change. If the script returns an undefined type instead of a string, the browser will not load a new page, with the result that the script simply runs against the current page content. This permits in-place font size and color changes, for example, without a page reload.

Usage

Bookmarklets are saved and used as normal bookmarks. As such, they are simple "one-click" tools which add functionality to the browser. For example, they can:

Modify the appearance of a web page within the browser (e.g., change font size, background color, etc.).

Extract data from a web page (e.g., hyperlinks, images, text, etc.).

Query a search engine, with search term(s) provided by previously selected text, or by a dialog box.

Submit the current page to a link validation service, or translation service.

"Installation of a bookmarklet" is performed by creating a new named bookmark in the toolbar, following the browser's procedure, and pasting the code into the URL destination field. The bookmarklet can then be run by loading the bookmark normally.

History

Steve Kangas of www.bookmarklets.com coined the term "bookmarklet," which he started to create based on an idea suggested in the Netscape JavaScript Guide. The term favelet was used early on by Tantek Çelik on 6 September 2001 (personal email). Brendan Eich, who developed JavaScript at Netscape, gave this account of the origin of bookmarklets:They were a deliberate feature in this sense: I invented the javascript: URL along with JavaScript in 1995, and intended that javascript: URLs could be used as any other kind of URL, including being bookmark-able.

In particular, I made it possible to generate a new document by loading, e.g. javascript:'hello, world', but also (key for bookmarklets) to run arbitrary script against the DOM of the current document, e.g. javascript:alert(document.links.href). The difference is that the latter kind of URL uses an expression that evaluates to the undefined type in JS. I added the void operator to JS before Netscape 2 shipped to make it easy to discard any non-undefined value in a javascript: URL. - Brendan Eich, email to Simon Willison