Key is stored only in this browser (localStorage), never sent anywhere but Twelve Data. Leave blank to run TQQQ/SPY/GLD in simulated mode.
BTC: live from CoinGecko, no key required. TQQQ / SPY / GLD: live from Twelve Data once a free key is saved above (~800 calls/day free tier; this page polls every 30s, well inside that limit). If a fetch fails — no key, rate limit, offline — that asset falls back to a simulated walk from its last real price, and its badge switches from LIVE to SIM so you always know which is which. Drawdown = decline from this session's high-water mark; amber flag at -10%, red at -20%.