Force Inclusion

Force inclusion is a protocol-level mechanism, most notably implemented in Ethereum via EIP-1559, that allows a transaction to be included in a block even if its attached fee is below the current prevailing market rate. Its primary purpose is to guarantee censorship resistance by preventing block producers from indefinitely ignoring valid transactions for economic or political reasons. A user can invoke this mechanism by submitting a transaction with a maxPriorityFee and maxFeePerGas of zero, signaling to the network that it must be included in a future block, typically within a predefined maximum delay.

The mechanism operates by leveraging the concept of a base fee. Under EIP-1559, each block has a dynamically calculated base fee that is burned. Transactions must pay at least this base fee. Force inclusion transactions pay only this mandatory base fee, offering no priority fee (tip) to the block producer. Validators are protocol-bound to include these transactions when the block's gas target is not full, ensuring the network's promise of credible neutrality. This creates a base fee auction for block space, where regular transactions compete with tips, while force inclusion transactions rely on protocol guarantees.

A critical technical requirement for force inclusion is that the transaction must be mempool-eligible and submitted from an Externally Owned Account (EOA). It cannot be a contract creation transaction. Furthermore, the mechanism includes a maximum wait time; on Ethereum, this is defined as 25 * MAX_BLOCK_GAS / GAS_LIMIT_PER_TX blocks, which translates to roughly 100 blocks or ~20 minutes under normal conditions. This prevents the mechanism from being abused to spam the network with zero-fee transactions indefinitely, as they are processed in a first-in-first-out queue within the constraint of the block gas limit.

The primary use case for force inclusion is censorship-resistant transactions, such as voting in decentralized governance, submitting fraud proofs in optimistic rollups, or executing critical smart contract functions during network stress. For example, in a Layer 2 rollup, a user can force-include a transaction to withdraw assets if the sequencer is maliciously censoring their requests. This makes force inclusion a foundational component for trust-minimized systems, ensuring that users always have a guaranteed, albeit slower, exit path that does not rely on the goodwill of block producers.

It is important to distinguish force inclusion from related concepts like fee bumping (RBF) or private transaction pools. While RBF allows a user to replace a pending transaction with a higher-fee one, force inclusion mandates inclusion at the base fee. Private pools allow transactions to bypass the public mempool but do not provide protocol-level inclusion guarantees. Force inclusion is thus a stronger, cryptoeconomic guarantee embedded in the consensus rules, making it a vital tool for maintaining the liveness and neutrality of decentralized networks.

Force Inclusion is a protocol-level guarantee that a valid transaction submitted to a sequencer or mempool will be included in a block within a specified time window, typically enforced by a challenge period or direct on-chain proof. This mechanism is a foundational component of censorship resistance, preventing centralized operators from indefinitely delaying or censoring user transactions. In systems like optimistic rollups, users can submit a transaction directly to the Layer 1 (L1) chain if the rollup's sequencer fails to include it, forcing its processing and ensuring the network's liveness guarantees are upheld.

The process is often triggered by a force inclusion transaction or a direct L1 submission. A user constructs a proof that their transaction is valid and was submitted to the sequencer but not included. They then pay the necessary L1 gas fees to post this transaction and its proof directly to the underlying blockchain's mempool. The L1 network's validators will then process it, effectively bypassing the potentially malicious or faulty sequencer. This acts as a powerful economic and cryptographic disincentive against censorship, as sequencers are compelled to include transactions promptly to avoid losing fee revenue to the more expensive L1.

Key parameters governing force inclusion include the maximum sequencing delay (the time a sequencer can delay a transaction) and the challenge period (the window for users to force inclusion). These are set by the protocol's governance or hardcoded rules. For example, a rollup might specify that any transaction not included within 24 hours can be forced onto L1. This creates a clear, predictable safety net for users and applications, ensuring state finality and operational reliability even if a primary processing layer behaves adversarially.

In practice, force inclusion interacts with other scaling mechanisms. In a validium (a zero-knowledge rollup using off-chain data availability), force inclusion may require proving data availability to the L1, which is more complex. Its implementation requires careful economic design to prevent spam attacks where users might force-include transactions to disrupt sequencing order. Despite this, it remains an essential cryptoeconomic tool, balancing scalability with the decentralized, permissionless ethos of blockchain technology by ensuring no single entity has absolute control over transaction ordering.