Transaction Fees

This page describes the different types of transaction fees that the Ethrex L2 rollup can charge and how they can be configured.

Priority Fee

The priority fee works exactly the same way as on Ethereum L1.
It is an additional tip paid by the transaction sender to incentivize the sequencer to prioritize the inclusion of their transaction.
The priority fee is always forwarded directly to the sequencer’s coinbase address.

Base Fee

The base fee follows the same rules as the Ethereum L1 base fee. It adjusts dynamically depending on network congestion to ensure stable transaction pricing.
By default, base fees are burned. However, a sequencer can configure a base fee vault address to receive the collected base fees instead of burning them.

ethrex l2 --block-producer.base-fee-vault-address <l2-base-fee-vault-address>

Operator Fee

The operator fee represents an additional per-gas cost charged by the sequencer to cover the operational costs of maintaining the L2 infrastructure.

This fee works similarly to the base fee — it is multiplied by the gas used for each transaction.
All collected operator fees are deposited into a dedicated operator fee vault address.

To set the operator fee amount:

ethrex l2 --block-producer.operator-fee-per-gas <amount-in-wei>

To set the operator fee vault address:

ethrex l2 --block-producer.operator-fee-vault-address <operator-fee-vault-address>

Fee Calculation

When executing a transaction, all gas-related fees are subject to the max_fee_per_gas value defined in the transaction.
This value acts as an absolute cap over the sum of all fee components.

This means that the effective priority fee is capped to ensure the total does not exceed max_fee_per_gas.
Specifically:

effective_priority_fee_per_gas = min(
    max_priority_fee_per_gas,
    max_fee_per_gas - base_fee_per_gas - operator_fee_per_gas
)

Then, the total fees are calculated as:

total_fees = (base_fee_per_gas + operator_fee_per_gas + priority_fee_per_gas) * gas_used

This behavior ensures that transaction senders never pay more than max_fee_per_gas * gas_used, even when the operator fee is enabled.

L1 Fees

L1 fees represent the cost of posting data from the L2 to the L1.
Each transaction is charged based on the amount of L1 Blob space it occupies (the size of the transaction’s stateDiff).

After each transaction is executed, the sequencer calculates the stateDiff generated by that transaction.
The L1 fee for that transaction is computed as:

l1_fee = blob_base_fee_per_byte * tx_state_diff_size

An additional amount of gas (l1_gas) is added to the transaction execution so that:

l1_gas * gas_price = l1_fee

This guarantees that the total amount charged to the user never exceeds gas_limit * gas_price, while transparently accounting for the L1 posting cost.
Importantly, this process happens automatically — users do not need to perform any additional steps.
Calls to eth_estimateGas already inherit this behavior and will include the extra gas required for the L1 fee.

The computed L1 fee is deducted from the sender’s balance and transferred to the L1 Fee Vault address.

The blob base fee per byte is derived from the L1 BlobBaseFee.
The L1Watcher periodically fetches the BlobBaseFee from L1 (at a configured interval) and uses it to compute:

blob_base_fee_per_byte = (l1_fee_per_blob_gas * GAS_PER_BLOB) / SAFE_BYTES_PER_BLOB

See State Diffs for more information about how stateDiffs works.

L1 fee is deactivated by default. To activate it, configure the L1 fee vault address:

ethrex l2 --block-producer.l1-fee-vault-address <l1-fee-vault-address>

To configure the interval at which the BlobBaseFee is fetched from L1:

ethrex l2 --block-producer.blob-base-fee-update-interval <milliseconds>

Useful RPC Methods

The following custom RPC methods are available to query fee-related parameters directly from the L2 node.
Each method accepts a single argument: the block_number to query historical or current values.