PreVerification Gas

PreVerification Gas (PVG) is a fee charged by a blockchain network or layer-2 rollup to cover the initial computational cost of validating a transaction's basic integrity before it enters the mempool or execution phase. This upfront payment acts as a spam-prevention mechanism, deterring users from flooding the network with invalid or computationally expensive transactions. By requiring this cost, the system ensures that only transactions with a genuine economic incentive proceed, optimizing node resources and maintaining network performance. It is a distinct fee from the standard execution gas paid for on-chain computation and state changes.

The PVG fee is typically calculated based on the intrinsic properties of a transaction, such as its size (calldata length), signature verification complexity, and other pre-execution checks. For example, in zk-Rollups like zkSync Era, PVG covers the cost of verifying cryptographic proofs and preparing the transaction for inclusion in a batch. This process is separate from the gas used to run the smart contract logic on the destination chain. If a transaction fails these initial checks, the PVG is still consumed, as the computational work has already been performed by the network's validators or sequencers.

From a user's perspective, PVG is often bundled into the total estimated transaction fee presented by a wallet. However, it represents a critical, non-refundable component that secures network health. Its implementation is particularly vital for Layer 2 solutions and high-throughput chains, where unchecked transaction submission could easily overwhelm system capacity. By economically aligning user behavior with network efficiency, PVG mechanisms protect against denial-of-service (DoS) attacks and ensure that block space is used responsibly, creating a more stable and predictable environment for all participants.

Preverification gas (PVG) is the portion of a transaction's total gas that is estimated and paid upfront to cover the computational cost of initial validation and signature checks before a transaction is included in a block. This initial validation, performed by nodes upon receiving a transaction, includes verifying the sender's signature, checking the nonce, and ensuring the account has sufficient balance to pay the maxFeePerGas * gasLimit. This upfront payment prevents spam by requiring a minimum economic commitment for network consideration, distinct from the execution gas used for running the smart contract code.

The process works by having the transaction sender specify a gasLimit and a maxFeePerGas. The network nodes multiply these values to determine the maximum transaction fee the sender is willing to pay. A portion of this maximum fee is consumed as PVG during the initial checks. If these basic validations fail—for instance, if the signature is invalid or the nonce is incorrect—the transaction is rejected, and the sender forfeits the PVG. This creates a cost for submitting invalid transactions, protecting the network from certain denial-of-service attacks.

It's crucial to distinguish PVG from the total gas used. The execution gas is only consumed if the transaction passes preverification and is executed within a block. The actual fee paid is gasUsed * baseFee + priorityFee, where gasUsed includes both execution gas and a smaller, fixed amount for intrinsic gas costs like data storage. Therefore, a transaction with high PVG costs might still have low execution costs if its logic is simple, but the sender must always have enough balance to cover the maximum potential fee (gasLimit * maxFeePerGas) at the moment of submission.

For developers, underestimating PVG requirements is a common cause of transaction failure. Wallets and libraries like Ethers.js or Web3.js automatically estimate a gasLimit that includes a safety margin for both preverification and execution. However, for complex transactions or during network congestion, manual adjustment may be necessary. A transaction will revert if the gasLimit is set too low to cover the PVG, resulting in an "out of gas" error before any contract code runs, emphasizing the need for accurate gas estimation strategies.

PreVerification Gas (PVG) is a deterministic gas cost calculated by an Ethereum node to cover the computational work of performing initial validation on a transaction before it is accepted into the mempool. This validation includes verifying the transaction's cryptographic signature, checking the nonce against the sender's current state, and ensuring the sender has sufficient balance to pay the maxPriorityFeePerGas and maxFeePerGas. Unlike execution gas, PVG is paid upfront and is not refunded, as the work is performed regardless of whether the transaction ultimately succeeds or fails during block execution.

The calculation is performed by the client software (e.g., Geth, Erigon) using a fixed gas cost schedule defined in the Ethereum protocol. Key components include a base cost of 21,000 gas for any transaction, plus additional gas for signature verification which depends on the transaction type: - 0 gas for a legacy transaction with a simple ECDSA signature. - 4,500 gas for an EIP-1559 transaction due to additional signature operations. - A variable amount for more complex account abstraction transactions involving EIP-4337 paymasters or signature aggregators. The node sums these fixed costs to arrive at the PVG total.

This gas is conceptually 'charged' against the transaction's maxFeePerGas limit during validation. If the calculated PVG multiplied by the maxFeePerGas exceeds the transaction's upfront payment (value sent with the transaction), the node will reject it immediately. This mechanism protects the network from Denial-of-Service (DoS) attacks by ensuring that spammers pay for the cost of initial validation, preventing the flooding of the mempool with invalid transactions that would waste node resources.