Simon Willison’s Weblog

The web's clipboard, and how it stores data of different types. Alex Harri's deep dive into the Web clipboard API, the more recent alternative to the old document.execCommand() mechanism for accessing the clipboard.

There's a lot to understand here! Some of these APIs have a history dating back to Internet Explorer 4 in 1997, and there have been plenty of changes over the years to account for improved understanding of the security risks of allowing untrusted code to interact with the system clipboard.

Today, the most reliable data formats for interacting with the clipboard are the "standard" formats of text/plain, text/html and image/png.

Figma does a particularly clever trick where they share custom Figma binary data structures by encoding them as base64 in data-metadata and data-buffer attributes on a <span> element, then write the result to the clipboard as HTML. This enables copy-and-paste between the Figma web and native apps via the system clipboard.