I genuinely cannot believe this 😭😭

I built an extension called SubChat a month back and today it sits at 120+ users and these 2 goats.

It’s basically a side widget which opens up if you have a question about any specific line anywhere. The good thing is that you don’t need to configure any API keys because it uses your current logged in Claude / Gemini.

You can check it out here

This took A LOT of time to build but I guess it was worth it.

Cheers!

Some of you might remember my posts from a couple of months ago about CPOS (Competitive Programming Operating System).

I originally built it because I was frustrated with my own competitive programming workflow.

I was using CPH for running/submitting code, a bunch of Codeforces tabs for problems, another tool for stats, another for rating predictions, and basically had no good way to figure out what I should actually solve next.

So I decided to build something that put all of that together.

My first post was basically: “I built a better CPH”

And honestly, I thought it would just be a fun side project.

That post ended up getting a lot more attention than I expected, so I kept building.

A few months later, CPOS has crossed 4,000 users.

That number is genuinely kind of insane to me.

What started as a small tool has turned into a full local-first competitive programming workspace:

• Browser extension for Codeforces/CSES/AtCoder
• VS Code extension for capturing problems, running samples and submitting
• Terminal UI for browsing problems, contests, analytics and recommendations
• Challenge with friends
• Codeforces profile analytics and progress tracking
• Rating predictions
• Problem recommendations based on your level and weak areas
• Codeforces themes / UI improvements
• In-browser editor
• Problem highlighting and annotations
• Contest notifications
• And a bunch of smaller things I've added based on what people have asked for

The part I'm happiest about is that it's still free, open source, and local-first. No accounts, no servers, no tracking.

Website: https://cpos.sohamaggarwal.com

GitHub: https://github.com/Soham109/cpos

For anyone who has used CPOS, I'd genuinely love to hear what you think.

What do you like? What sucks? What should I build next?

And if you were one of the people who tried it when it was still a tiny 4-day project, thank you. A lot of the features that exist today came directly from feedback on those first posts.

Still have a ridiculous number of things I want to build for this.

Thanks for 4,000+ ❤️

Highlighting something confusing and alt-tabbing to an AI tab, pasting, adding context… I did it 30 times a day, so I built SubChat to kill that loop.

Select any text → a little "Ask" button appears → a side-chat opens right there. It runs on your own logged-in claude.ai / ChatGPT / Gemini session, so there's no API key and no extra token bill — it's just the subscription you already pay for.

• Works on any page (articles, docs, PDFs, dashboards)
• Free tier: 10 subchats/day, no account, nothing leaves your machine except the prompt to your AI
• Pro adds unlimited + whole-page context + "web mode"

Store link: https://chromewebstore.google.com/detail/subchat-%E2%80%94-inline-follow-u/nmbmgjgehmpopilieoojidjcpiegkgoc

Would love feedback on the UX — especially the highlight→ask gesture.

·

My last post blew up and hit 27k+ views (achieved #1 trending on r/codeforces).

CPOS (Competitive Programming OS) now has 200+ active users. If you missed it: here's the original post.

I spent the last few weeks talking to users, looking at what other tools miss, and building a proper v2. Here's everything new — it's still 100% free and open source.

If you want to know about CPOS in more detail, please read this Codeforces blog instead (Please upvote it, I somehow have negative contributions T_T).

1) Chrome Extension (biggest update)

Link for the chrome extension

Codeforces (and CSES) rethemed:

• 5 built-in dark themes + a fully custom accent color picker
• "Modernize" mode: cleaner layout, better typography, tighter spacing — same CF, just not 2009

Problem pages:

• Browser-based IDE — write, run, and submit without leaving the tab
• Highlight and annotate problems (personal notes, saved locally)
• Expand view: collapse the sidebar to focus on the problem
• Per-problem timer

Problemset page:

• Hide solved problems
• Filter by difficulty and tags
• Per-problem sparkline showing your rating at the time you solved it

Standings:

• Filter standings by language
• Color-coded rows by language used

Profile:

• Upgraded analytics dashboard
• Compare your profile head-to-head against any other user

Other:

• Contest reminders
• Daily problem
• Favorites list
• Rank delta predictor for ongoing contests - basically carrot.

2) VS Code Extension

• View the problem statement directly inside VS Code — no browser tab needed
• See a reference solution via Google search (disabled during live contests)

3) TUI

• New Target tab: set a goal rating and get problem recommendations based on your actual weak topics and solve history

Everything is free, no account needed, no telemetry. If you find it useful, GitHub Sponsors would mean a lot. Please also share this with your friends who use codeforces if you liked it!

=> cpos.sohamaggarwal.com — all download links and docs there.
=> Join the CPOS discord server here

Happy to answer questions or take feedback below.

PS: If you are someone who might be interested in helping me make a 2/3 minute professional demo video for this, please hit me up!

Hey everyone,

I built CPOS.

Instead of having practice scattered across browser tabs, terminal commands, CPH, spreadsheets, and rating pages, CPOS puts the workflow in one place.

It currently supports:

• Codeforces + CSES problems
• capturing problems locally
• auto-creating solution files
• running samples
• submitting solutions
• viewing upcoming/live contests
• tracking progress
• weak-tag analysis
• recommending unsolved problems around your level
• VS Code + Chrome extension support

It is kind of inspired by the CPH workflow, but extended into a fuller practice and progress-tracking system.

Links:

Website: https://cpos.sohamaggarwal.com
GitHub: https://github.com/Soham109/cpos
VS Code Extension: https://marketplace.visualstudio.com/items?itemName=sohamaggarwal.cpos-vscode
Chrome Extension: https://chromewebstore.google.com/detail/gjnbapmjonegeeamdeahcoojgokeogmm

I would really appreciate feedback, feature requests, bug reports, or criticism.