The cost of the currency you were never quoted in. Use for "what does it really cost me
to trade $5M of SOL", "which venue is cheapest for a USD fund", "how much am I paying to
hold USDT", "should I use a USDC venue instead".
THE POINT: every execution cost in this API, and in every competing tool, is denominated in
the VENUE'S OWN quote currency. Most perp venues quote USDT. A fund's money is USD. So the
quoted cost is for a trade the fund cannot place until it has bought USDT, and the price of
that conversion appears in nobody's TCA. This walks the live USD/USDT and USD/USDC books at
the caller's size, reports the cheapest round trip and the capacity ceiling, and re-ranks
venues on cost INCLUDING the leg.
IT DOES NOT TELL YOU WHICH VENUE TO TRADE ON, and you must not present it as if it does.
That output existed, was measured across 20 coins x 5 sizes, flipped 0 of 95 times, and was
deleted — `leg_does_not_change_venue` in the response carries the numbers. What it tells you
is what the trade ACTUALLY costs: quote `leg_as_pct_of_execution_cost`, which is the leg
measured against the trade's own execution cost on the venue the desk would really use.
THE LEG IS A COST ON CAPITAL MOVED, NOT ON TURNOVER. `turns` is how many times the desk
turns the balance over before repatriating to USD. At turns=1 the full round trip is
charged; at turns=50 the leg is rounding error and the response will show that. Do not
quote the turns=1 figure as a per-trade cost for a desk that trades continuously.
`coin` = ticker e.g. 'sol'. `notional_usd` = order size in USD. `side` = 'buy' or 'sell'.
Requires an EnsoTrade Pro API key.