PyScript lets you run Python scripts right in the browser, side by side with JavaScript, with two-way interaction between your code and the web page.

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.

Playwright, a Python library, allows developers to essentially control the browser with a few lines of Python code to automate cross-browser testing for single-page web apps and Progressive Web Apps.