Bookmarklet

A bookmarklet is a bookmark stored in a web browser that contains JavaScript commands that add new features to the browser.

They are stored as the URL of a bookmark in a web browser or as a hyperlink on a web page. Bookmarklets are usually small snippets of JavaScript executed when the user clicks on them. When clicked, bookmarklets can perform a wide variety of operations, such as running a search query from selected text or extracting data from a table.

The code given here is a variation of the Vignere Cipher.

Upon clicking this bookmarklet, the code is copied.

I then simply run the code in the console to get flag.