[myfonj]

You can make folks test it in their browsers by instructing them to copy and paste dataURI into their URL bar, like:

    data:text/html,<link rel="icon" href="https://zany.sh/favicon.svg?text=hi">

This one for example shows nearly invisible text in dark theme for me.

Or maybe add text input to dynamically update current page's favicon to see the outcome instantly.

[jchap]

this is a great idea, going to update the docs. also, regarding dark themes, you can control the text/background color via query params:

    <link rel="icon" href="https://zany.sh/favicon.svg?text=hi&background-color=black&text-color=white">