Several of the Scratch 3.0 extensions (for example micro:bit) require to install some piece of software, called “Scratch Link”. Is this “Scratch Link” available for all platforms, including Linux?

The topic of writing and installing one's own custom Scratch 3.0 extensions is still shrouded in mystery, but perhaps some clarity can be given.

I am wondering how the web browser <=>local hardware communication is established. I could guess that this Scratch Link application exposes Bluetooth (and perhaps also USB?) operations through http/sockets API (so that it becomes accessible from the web browser environment), but is there any documentation/reference about what it does? If this is not openly documented, then such exposure could be considered a pretty serious security risk.

Should the Scratch Link operation be openly documented, that would let me to write my own http/sockets server and use the said micro:bit extension to access my own custom hardware projects, say, send and read MIDI data. Scratch would never know it is not talking with something else at the other end.

A lot of us are waiting for Scratch to open up access to writing and using our own extensions.

However, they are being quite reluctant to do so.