PyScript, which is, of course, Python in the browser. The tool is in the early experimental phase, so the project doesn’t suggest using it in a production environment yet.

Anaconda, makers of the Python distribution for scientific computing, announced at PyCon US 2022 the PyScript project — an in-browser, single-include way to run Python scripts in HTML pages as ...

It's possible to take a step further with a browser extension, but this is a basic Python project that hosts a web page that you can drag and drop a file on for a visualizer.