BTC perpetual futures order book liquidity resting within ±1% of the mid price (bid + ask, in USD), averaged from snapshots taken roughly every 25 seconds on Binance. This is the liquidity market makers are actually quoting — the actual depth behind the price, not a proxy for it.

When this liquidity thins out, the book has become fragile even before price moves: a given order size will push the price further than it would against a deep book. Book Imbalance (bid minus ask, normalized) shows which side currently has more resting size.

Not available from any live public API: Binance's real-time order book endpoint only reaches about ±0.17% of the mid price, not enough to measure this. Sourced from Binance's historical book-depth archive, about 1 day delayed.