Fees are collected strictly on-chain by the shield-pool program into the mint-scoped treasury
PDA, using the fixed and variable fee stored in each pool’s PoolConfig. No other component
assesses or deducts fees.
Fees apply only to flows that move value out of the pool (publicAmount < 0: withdrawals and
swaps). Deposits and shield-to-shield transfers charge no fee.
Constants
- SOL pool fixed fee:
5_000_000 lamports (0.005 SOL)
- SPL pool fixed fee (USDC/USDT):
450_000 base units (0.45 USDC / 0.45 USDT), charged in
the withdrawn token
- Variable fee (all pools):
gross * 3 / 1000 (0.30%)
- Minimum deposit:
10_000_000 lamports (0.01 SOL) on the SOL pool; 1_000_000 base units
(1.00 USDC / 1.00 USDT) on the SPL pools
Per-flow behavior
- Deposit (
publicAmount > 0): no fee. The full deposit amount moves into the pool and the
output commitments encode the full amount.
- Shield-to-shield transfer (
publicAmount = 0): no fee. No external value moves; the output
commitments sum to the inputs.
- Withdrawal (
publicAmount < 0): the destination receives net = gross - fee; the treasury
PDA receives fee.
- Swap (
TransactSwap, SOL pool only): fee = fixed + variable is taken from the gross SOL
at the first transaction; the remainder (gross - fee) is what gets swapped.
Fee math
SOL pool (withdraw/swap):
SPL pools (withdraw):
Worked examples
Withdraw 1 SOL (1_000_000_000 lamports) gross:
- Fixed:
5_000_000 lamports
- Variable:
1_000_000_000 * 3 / 1000 = 3_000_000 lamports
- Fee:
8_000_000 lamports — net to recipient: 992_000_000 lamports
Withdraw 100 USDC (100_000_000 base units) gross:
- Fixed:
450_000 base units (0.45 USDC)
- Variable:
100_000_000 * 3 / 1000 = 300_000 base units (0.30 USDC)
- Fee:
750_000 base units (0.75 USDC) — net to recipient: 99_250_000 base units
The Cloak app presents this in reverse: the user enters what the recipient should receive, and
the app grosses up so net equals the entered amount. At the program level the invariant is
always net = gross - fee.
