A bookmarklet is a little piece of bookmarkable javascript code that can be used to automate the browser in various ways.

The definitive list of bookmarklets can be found at bookmarklets.com

See also Bookmarklet As Intermediary

Tips

• Use void to discard results of an expression, otherwise they may be displayed in the current window
• Beware of frames
• Use maximum of ~500 characters unless you use a Bookmarklet Bootloader
• Use prompt to grap single line of input (possibly multiple times)
• Use DOM to get access to complete page, and fall back to regexps to parse additional content
• You can add elements to the DOM, including new attributes, CSS styling and event handlers thereby enriching the original page.
• Provide different versions of a bookmarklet for different browsers, rather than including browser sniffing directly in the bookmarklet. It'll bloat the code.
• Udell has an example of setting a cookie from someone elses domain. Hmmm....

MT Bookmarklets aren;t that clever. They just grab the currently selected text (if any), the window title and current location and pass those as parameters to an MT page viewed in a separate window.

Links

• XML-RPC Message Builder -- make XML-RPC messages from Javascript. Back-ended by a PHP server that turns XML-RPC responses into javascript strings for feeding back into the browser.
• Interfacing Annotea via JavaScript
• Javascript RDF Parser
• JasMin -- Minimal XML parser
• Sarissa -- "Sarissa is a JavaScript library that provides a common interface between similar DOM extentions of browsers, including loading of DOM objects from remote sources or Strings, XSLT transformations etc"