Determine technology a site is built with programmatically online

I basically want to do the same thing as this guy: How do you determine what technology a website is built on? except I want to create a web app that will spit out the answer to someone if they enter in a URL. I'm essentially trying to make something very similar to builtwith.com, except I will be looking for different things than builtwith.com will be.

Couple of details:

• I'm familiar with Python so a solution that uses Python would be best.
• I already know how to use Python to look at a site's source code. That helps. But I also need to be able to see all the HTTP requests the site is making (for example, a call to analytics.js). I know selenium can do this with a proxy, but this should be running as a web app that anyone can use.

I've spent a lot of time trying to figure this out, and I'm still coming up short.