Up or Down

A real-time Bitcoin price guessing game. Predict whether BTC/USD will be higher or lower after 10 seconds and earn points.

Live demo: up-or-down-eight.vercel.app

Functionality

Players are shown the latest BTC/USD price and a 10-second countdown. Before the countdown ends, they submit a guess: UP or DOWN. When the timer hits zero, the new price is fetched and compared to the price at the time of the guess:

• Correct → +1 point
• Wrong → −1 point

After 3 seconds the result clears and a new round begins automatically. Only one guess can be active at a time.

Each player is identified by a UUID stored in localStorage, so scores persist across browser sessions: close the tab and come back, your score is still there.

Design

Check the Figma. I designed the UI in Figma after a short but effective UX research phase: I looked at a potential user persona and studied existing products in the space like Kalshi and Polymarket.

Tech stack

Layer	Choice
Framework	Next.js 16 (App Router)
Styling	Tailwind CSS
DB ORM	Drizzle ORM
Database	AWS RDS PostgreSQL
Data fetching	TanStack Query
Price feed	Binance REST API (GET /api/v3/ticker/price?symbol=BTCUSDT)
Chart	wani-graf (my product, embedded via iframe)
Deploy	Vercel

Local setup

Prerequisites: Node.js 18+ and npm.

git clone <repo>
cd up-or-down
npm install

Copy the example env file:

cp env.local.example .env.local

Open .env.local and replace YOUR_PASSWORD in DATABASE_URL with the actual password — ask the project owner.

The RDS SSL certificate is already committed at certs/rds-ca.pem, no extra setup needed.

npm run dev

Open http://localhost:3000.

Environment variables

Variable	Description
DATABASE_URL	Postgres connection string (ask project owner for password)
NEXT_PUBLIC_APP_URL	App base URL

Database

Schema is defined in src/lib/schema.ts. DB client is in src/lib/db.ts.

The AWS RDS CA certificate is committed at certs/rds-ca.pem — no manual setup needed, Drizzle uses it automatically for secure SSL connections.

# generate a migration after changing schema.ts
npm run db:generate

# apply migrations to the DB
npm run db:migrate

Migrations live in ./drizzle/. Never edit them by hand.

Deploy to Vercel

1. Push to GitHub.
2. Import the repo at vercel.com/new.
3. Under Settings → Environment Variables, add:
   • DATABASE_URL — your RDS connection string
   • NEXT_PUBLIC_APP_URL — your Vercel deployment URL (e.g. https://up-or-down.vercel.app)
4. Make sure the RDS security group allows inbound connections on port 5432 from 0.0.0.0/0.
5. Hit Deploy.

The vercel.json at the repo root is already configured — no extra setup needed.

API routes

Method	Path	Description
GET	/api/price	Live BTC/USD from Binance
GET	/api/score?id=	Get player score
POST	/api/score	Save player score (body: { id, score })

Deployment notes

Binance API and US IP geo-blocking

Binance (binance.com) blocks API requests from US-based IP addresses for regulatory reasons — the exchange is not licensed to operate in the United States and tightened geo-blocking following its 2023 FinCEN/DOJ settlement. Requests from US datacenter IPs return HTTP 451 Unavailable For Legal Reasons.

The vercel.json at the repo root pins all functions to Vercel's Stockholm region (arn1), which avoids the Binance block and co-locates the functions with the AWS RDS instance (also in eu-north-1), reducing database latency. No extra configuration needed — it's already committed.

Possible extensions

Timers could move to the server for tamper resistance and consistent timing. Score validation could also live on the server so the game logic is not entirely client-driven. For a small app, client-side timing is fine; scaling would warrant server-side rounds and scoring.