I suggested to an installer yesterday that writing down my new router's credentials would be better served with a WiFi QR Code instead.
He took the idea back to his company.

In the meantime I realised there are people out there doing the same thing with offered on-line utilities.
The problem with these is you might be sharing your secure credential to someone other than your invited guests.

Xara to the rescue.

Xara - Wifi QR Code Generator.xar uses Xara's Third-Party QR Code Generator, which is naff but works well enough for this.
I threw in a Bitmap Copy and Live Copies to fill a page for printing.

The instructions and guide are off-page.

If you want an on-line version, this https://qifi.org is SSL-secure and promises no data transfer off your computer.
I also have my Android barcode scanner set not to open web pages automatically.

Secretum tuum custodi.

Acorn