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providers.md

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+# Providers & symbol formats
+
+## Stocks / ETFs / Indices (default: Yahoo via yfinance)
+Pros:
+- Very broad symbol coverage, no API key.
+Cons:
+- Unofficial access patterns can be rate-limited or break.
+
+Common examples:
+- AAPL, MSFT, TSLA
+- Indices: ^GSPC (S&P 500), ^DJI, ^IXIC
+- ETFs: VOO, SPY, QQQ
+
+## FX (default: ExchangeRate-API Open Access)
+Endpoint: https://open.er-api.com/v6/latest/<BASE>
+- No API key
+- Updates once per day
+- Rate-limited
+- Attribution required by their terms
+
+Symbol formats accepted by this skill:
+- USD/ZAR
+- USDZAR
+- GBP-JPY
+- EURUSD
+
+We normalize to BASE/QUOTE and fetch BASE->all then pick QUOTE.
+
+## Why not exchangerate.host by default?
+It now requires an API key for most useful endpoints and has limited free quotas, so it’s not a great no-key default.
+
+## Paid providers (optional future upgrade)
+If you need many symbols or frequent polling:
+- Twelve Data
+- Alpha Vantage
+- Polygon
+- Finnhub
+
+This skill includes environment variable placeholders, but does not implement these providers yet.