RSI API Guide for ETF and Investment Apps

The Relative Strength Index is a bounded momentum indicator commonly calculated over 14 periods. It compares smoothed average gains with smoothed average losses and returns a value between zero and 100.

Initial averaging, Wilder smoothing, adjusted closes, and missing sessions all affect the output. An API should document these choices and return the calculation period and source date with the value.

Thresholds such as 70 and 30 are descriptive conventions, not guaranteed buy or sell signals. Pair RSI with price context, trend measures, and explicit risk disclosures in user-facing products.