A momentum oscillator from 0 to 100 measuring the speed and strength of price moves — above 70 is overbought, below 30 oversold.
The Relative Strength Index (RSI), developed by Wilder, is a popular momentum oscillator usually computed over 14 sessions. It ranges 0-100: above 70 is considered overbought (a pullback is possible), below 30 oversold (a bounce is possible). On its own it is not a buy/sell trigger — in strong trends RSI can stay above 70 for a long time. Its most useful signal is divergence: when price makes a higher high but RSI makes a lower high, momentum is weakening. FoudaLens computes RSI for every stock among the indicators on the stock page.