As a (former) reporter, site monitoring is a big part of what I do on a daily basis and I used many, many such services.

I can attest that, at least from the landing page, this seems to be a very good execution of the concept, especially the text-based diffing to easily spot what changed and, most importantly, how.

The biggest hurdle for such apps however are 'js-based browser-rendered sites' or whatever they're called nowadays. How does Site Spy handle such abominations?

Thanks, that’s a really good question. Site Spy uses a real browser flow, so it generally handles JS-rendered pages much better than simple HTML-only polling tools. In practice, the trickier cases tend to be sites with aggressive anti-bot protection or messy login/session flows rather than JS itself. I’m trying to make those limitations clearer so people don’t just hit a vague failure and feel let down