Range Expansion & Contraction API

The volatility-coiling setups breakout traders hunt, computed live from Yahoo Finance daily OHLC — no key, nothing stored. Markets do not trend or chop at random: tight-range days cluster and precede expansion, and the classic edge — Toby Crabel's NR7 (the narrowest daily range of the last seven), the inside day (a bar wholly inside the prior one) and the outside day (a bar that engulfs it) — is that a coiled spring releases. This API measures the coil and the release. For each instrument it returns today's range as a percentile of its recent range (low = contracted/coiling, high = already expanded), whether today is an NR7, NR4, inside or outside day, the average daily range, and the historical frequency of each setup. Crucially it also returns the follow-through: after an NR7, how often the next day broke the NR7 day's high or low and how often its range expanded — the base rate that tells you whether the coil is worth trading. The asset endpoint returns one instrument's full range profile; the screener endpoint ranks the universe by contraction (most coiled, lowest current range percentile — the breakout candidates) or by realised range. This is the range-contraction / NR7 breakout-setup cut — distinct from the candlestick-pattern API (named reversal/continuation shapes, not range size), the volatility dashboard (level, not the coil), and the gap and price APIs. It is the squeeze before the move.