Quant Practice

Mental math drills, an inventory-aware market-making simulator, and a probability/stats problem bank for quant trading interview prep. Spun out from the portfolio site so it can grow independently behind auth.

The drills

1. Mental Math Trainer — timed arithmetic drills (configurable operations, digit sizes, round length) plus a sequences/pattern-recognition mode.
2. Market-Making Game — the "make me a market" game from real trading interviews (Jane Street, Optiver, ...) in three flavors: card game, dice game, and Fermi estimates. You quote a two-sided bid/ask on a hidden total across rounds while information is revealed, against a counterparty that trades when it's profitable.
3. Probability & Stats — a LeetCode-style problem bank: browse by index/title/ difficulty (★–★★★), filter by category, submit answers (decimals, fractions like 6/91, or expressions like (4/9)^4 all accepted), with optional hints and full KaTeX-rendered solutions. Problems are authored in curated batches — each question written in original wording, solved, and verified numerically before import. A per-problem flag button lets users report suspect answers/parsing while the bank matures.

Scores and attempts persist per-user (Supabase), and /profile shows per-drill stats including a cross-user percentile.

Stack

• Next.js 16 (App Router, Turbopack) + TypeScript + Tailwind CSS v4
• Supabase: Google OAuth sign-in + Postgres (attempt history, problem flags)
• KaTeX for math rendering

Setup

1. Create a free project at supabase.com.
2. In the Supabase dashboard, go to Authentication → URL Configuration and add http://localhost:3000/auth/callback (and your production URL's /auth/callback once deployed) to the redirect allow list. Then under Authentication → Providers, enable Google (create an OAuth client in Google Cloud Console and paste the client ID/secret — Supabase shows the exact redirect URI to use).
3. Run each file in supabase/migrations/ (in order) in the dashboard's SQL Editor — they create the drill_attempts table, the percentile RPC, and the problem_flags table.
4. Copy .env.local.example to .env.local and fill in the values from Project Settings → API:

   NEXT_PUBLIC_SUPABASE_URL=...
   NEXT_PUBLIC_SUPABASE_ANON_KEY=...
   NEXT_PUBLIC_SITE_URL=http://localhost:3000
   

5. Install dependencies and run the dev server:

   npm install
   npm run dev
   

6. Visit http://localhost:3000, sign in with Google, and open /practice.

The app degrades gracefully without a Supabase project: drills work, but sign-in and score persistence no-op.

The probability problem bank

Problem content lives in the Supabase problems table, not in this repo (fields: id, source, chapter, difficulty, category, title, question, hint, answer_type, answer, tolerance, solution, tags — questions/hints/solutions support KaTeX $...$ and $$...$$). Batches are authored locally in a gitignored staging file and upserted with scripts/migrate-problems.mjs.

Content policy: no fabricated problems, and no problem text reproduced verbatim from any source. Every question is written in original wording, and every answer is verified numerically (exact computation or simulation) before it's upserted. Solutions and hints are original. Answers and solutions never leave the server — checking goes through the check_answer / reveal_solution RPCs (see supabase/queries/problem_bank_review.sql for how flags + solve stats are reviewed).

Deploying

Deploy to Vercel (connect this repo) and set the same three env vars in the Vercel project settings. Update the Supabase redirect allow list with your production /auth/callback URL, and set NEXT_PUBLIC_SITE_URL to your production domain.

Roadmap ideas

• More problem-bank batches (conditional probability, expectation games).
• Leaderboard across drills — requires moving answer checking server-side first.
• Spaced-repetition resurfacing of missed problems.

License

Code is MIT-licensed. Problem-bank content (questions, solutions, hints) is not part of this repository — it lives in the app's database and is meant to be practiced against in the app rather than repackaged. src/data/fermi_questions.json contains factual reference values with verification noted inline.