Codeforces Upsolve Tracker

What is Codeforces Upsolve Tracker?

I created this website which gives me a list of problems that I haven't upsolved and ta-da now I can revisit those problems and learn from them. How am I filtering these problems? 1. Fetch all the official contests you participated in last 6 months (who even cares before that). 2. In those contests, find all unsolved problems whose rating lies <= (peak rating + 200). 3. Skip problems whose rating isn't defined as of now