Fees
Aztec transactions pay fees in Fee Juice.
aztec-rs exposes several fee payment strategies via the aztec-fee crate.
Context
Not every user has Fee Juice on the account they are acting from. Aztec supports sponsored and delegated payment flows to handle onboarding and UX smoothly.
Design
Shipped strategies (implementors of FeePaymentMethod):
NativeFeePaymentMethod— the sending account pays directly in Fee Juice.SponsoredFeePaymentMethod— a public sponsor contract pays unconditionally.FeeJuicePaymentMethodWithClaim— the account first claims Fee Juice from an L1 deposit, then pays.
Private FPC support is planned but not yet shipped in aztec-fee; consumers needing that flow must implement FeePaymentMethod themselves.
Implementation
See aztec-fee for payment-method builders and the
aztec-ethereum FeeJuicePortal helpers for L1 deposits.
Edge Cases
- A transaction that deploys the paying account itself MUST use a strategy that doesn’t presume prior deployment.
- Sponsored flows MUST budget for simulation variance between estimate and actual gas.
Security Considerations
- FPC contracts may refuse service for any reason; applications must handle rejection.
- Claim messages MUST be cleared from the L1 portal to prevent double-claim.