UPDATE 2:
Saving codeforces questions for revision and upsolving is now live on the website.
Sign in with google so that no one else has access to your personal revision list.
Link your account to your codeforces handle by submitting a compilation error within 60 seconds.
Now you have access to create and edit your upsolve list. Add problems by just pasting a codeforces problem link and it will fetch the problem for you!
UPDATE 1:
There has been an overwhelming response from users worldwide, and I am very grateful for the same. I also received valuable feedback from a lot of you, and have tried implementing changes in the recommendations being made for every user.
Based on your feedback the recommendation model has now been improved (took a lot of tinkering). You might notice a slight change in the order/types of problems being recommended to you compared to before. Here are the statistics on the changes I have implemented: 
Original post
I'm currently a pupil on Codeforces, and like many others at this stage, I've always struggled with choosing the right problems to solve. There are a lot of great problemsets/ladders/sheets out there, but most of the time I find myself wondering what should I solve next?
Jumping between problems that are either too easy or way too hard -- I wanted something that could understand my current level, know what I'm weak at, and recommend problems that would genuinely help me grow — not just based on rating, but also based on me.
That was my motivation to build CF Recommender. It analyzes your Codeforces submissions and gives you a list of problems (Tailored to your real performance): 
Focused on topics you struggle with: 
Balanced in difficulty — not too easy, not discouragingly hard
Just open the tool, enter your handle, and it’ll do the rest.
Why I’m sharing this
This project was born from my own frustration — but I know I’m not the only one who feels this way. So I’d love it if you could try it out and tell me:
- Did the recommendations feel useful?
- Did it help you focus better?
- If you find any bugs or missing functionalities
Marking the link again here: https://cfrecommender.vercel.app/
Whether you’re a newbie or an expert looking to practice smarter, I’d be grateful if you gave it a shot and let me know what you think — either here in the comments or through the feedback option in the tool.
Looks really cool! Would 100% use this
really insane, well done
Good stuff, the recommended problems are very nice too.
Although, are the weak topics just the topics on cf on which I have the least problems solved on? Another way you could tweak is by taking an average AC to submission rate for each topic and then recommending the lowest ones, while excluding those topics which have <20ish submissions, such as string suffix structures or MITM
Thank you so much for the kind words! Also, the weak topics do consider the problems least solved, but also some other factors like your current level, past levels etc. Formulating a good heuristic for weak topics was something I was struggling on... Tried the heuristic you suggested but it wasn't working well for higher rated users.
Will work more on it though! Thanks a lot, do leave some feedback too!
Checked it out on mobile. Looks neat, nice UI. However the proficiency measurement lacks accuracy, topics that many people of x rating can do, but you do little of should count as weak proficiency. In my instance I do few do problems (actually I tend to avoid pure dp), yet it considers dp a strength. Though there may be a different reason for this.
Many problems which have both the greedy and dp tags should not contribute to dp proficiency imo, because most people do it with greedy, the do could just be a pref sum or something.
Other than that cool idea and project!
why's it showing authentication error?
I have 600+ submissions bruh
Edit: It is working now
The UI looks nice and the idea is great, will definitely use
Wonder what algorithm you use lol