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Fee Structure

TL;DR

Darknyx charges a flat protocol fee in basis points (for example, 30 bps). Both sides of a trade pay their own fee. Each order pre-funds its fee as part of its collateral, and the fee is collected at settlement as a fee note minted to the protocol, so fees, like everything else, settle privately on-chain.

The fee model​

Every trade pays a protocol fee proportional to its value:

fee = trade_value × fee_rate_bps / 10_000

Two principles define how it is applied:

  • Both legs pay. The bid and the ask each pay a fee on their own side of the trade. There is no maker rebate or taker surcharge, because a batch auction has no maker/taker roles (see Clearing Price).
  • The fee is pre-funded. An order must lock enough collateral to cover both its nominal cost and its own fee. The required collateral is:
required collateral = nominal cost + fee

where the nominal cost is amount × price_limit for a bid (quote units) or amount for an ask (base units). The engine derives this at intake. If an order's collateral note does not cover it, the order is rejected as conservation-breaking rather than allowed to under-pay.

The SDK handles fee-inclusive collateral

You do not compute the fee yourself. The SDK sizes an order's collateral note to cover the nominal cost plus the fee, so the order passes the conservation check. This is also why a place-order request is fully collateralized up front: the fee is already accounted for in the note you deposited.

How fees are collected​

Fees are collected at settlement, in the same atomic, proven step as the rest of the trade. When a batch settles, the output notes include the protocol's fee notes, one per asset side, minted alongside the traded asset and any change note. There is no separate fee transaction and no off-chain fee accounting: the fee moves as a note, on-chain, under the same zero-knowledge proof that gates the trade.

Because the fee is charged on the actual cleared amount, an order that locked fee-inclusive collateral on its worst-case (limit) price and then fills at a better clearing price gets the surplus back as part of its change note. You never overpay the fee on price improvement.

Worked example​

Suppose the fee rate is 30 bps (0.30%) and you place a bid to buy 10 base at a limit of 150 quote each:

nominal cost   = 10 × 150        = 1500 quote
fee            = 1500 × 30 / 10_000 = 4.5 quote
collateral     = 1500 + 4.5      = 1504.5 quote   ← what your note must cover

If the batch clears at 148, you pay 1480 for the fill, your fee is charged on the cleared amount, and the difference comes back to you as a change note, all in one settled, proven step.

Why fees settle as notes​

Collecting fees as on-chain notes keeps the whole system consistent: there is one value-movement mechanism (notes, gated by proofs), one place fees are visible (the public transparency reserves, which account for every mint including the protocol's), and no privileged off-chain ledger. Fees are as private and as verifiable as trades.

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