A perpetual future never expires, so something has to keep it tethered to spot. That something is funding: a payment made directly between longs and shorts, usually every eight hours. When the perp trades above spot, longs pay shorts. When it trades below, shorts pay longs.
The number is small - often a few thousandths of a percent - but it is paid repeatedly, and annualising it makes the message obvious. Funding of 0.01% every eight hours is roughly 11% a year to hold a position. At 0.08% it is over 85%.
What it actually tells you
Funding is a price for crowding, not a forecast. High positive funding means longs are numerous and impatient enough to pay for the privilege. That is not bearish on its own - trends run for a long time on positive funding - but it does say who is exposed if the tape turns, because the side that is paying is the side that gets liquidated.
The useful signal is rarely the level. It is the extreme relative to that venue's own recent history, and it is the disagreement between venues.
Never average the venues
This is the mistake most tools make. Binance, Bybit, OKX, Kraken, Hyperliquid and dYdX have different participants, different collateral rules and different funding intervals. When one pays 60% annualised and another pays nothing, the gap is the read. Averaging them produces a single number that describes no market that exists.
The Crypto Market Map shows funding per venue and never blends it, alongside the open interest that says how much is actually riding on it.