Immutables via Salt
Aztec contracts can commit immutable values directly into the contract's address by encoding them into the deployment salt, removing the need for a separate initialization transaction.
The aztec-immutables-macro repository was archived in July 2026 and receives no updates. Before you depend on it, check that it builds against your Aztec version. The technique this page explains, encoding immutables in the deployment salt, still applies.
Overview
Rather than storing immutables in private storage (which requires an initializer function and an extra transaction), the aztec-immutables-macro library encodes them into the contract's salt:
salt = poseidon2_hash([actual_salt, constant_0, constant_1, ...])
Since the salt is part of the address derivation, the immutable values become cryptographically bound to the contract's address itself.
Key benefits
- No initialization transaction — immutables are committed at deployment time, not in a separate setup call
- Runtime verification — at execution time, capsule data is loaded and verified against the stored salt, ensuring data integrity
- Persistent storage — immutables are persisted to the PXE's CapsuleStore after deployment, so capsules don't need to be attached to every transaction
- Compatible with standard storage — works alongside
#[storage]and initializers when needed
Performance
Initialization cost is completely eliminated (no constructor transaction). The per-transaction overhead is approximately 1,098 gates (+0.2%) in the account entrypoint.
Getting started
For installation instructions, usage examples, and a reference implementation of an initializerless Schnorr account contract, see the aztec-immutables-macro README.