Mempool explorer launches service to expedite unconfirmed bitcoin transactions via five mining pools

Bitcoin blockchain explorer Mempool has launched an off-chain service that aims to help users expedite unconfirmed transactions by paying an extra miner fee and service charge.

Known as Mempool Accelerator, the service will get “stuck transactions confirmed by paying an out-of-band fee,” the project noted. Users can locate a transaction on mempool.space, select the accelerate option from the transaction page and pay in bitcoin via Lightning or fiat via Cash App, Apple Pay or Google Pay with no sign-up process.

There are five initial mining pool partners for the service: Foundry USA Pool, MARA Pool, SBICrypto, SpiderPool and Ocean Pool, which account for around 40% of Bitcoin’s global hashrate, according to the firm.

Mempool sends the acceleration request to its mining pool partners, which can then choose to expedite the transaction based on a new accelerated fee rate. The transaction is not replaced; it is simply treated by those mining pools as having a higher fee, increasing the chances of it being confirmed in the next block, though this is not guaranteed. Bitcoin applications can also integrate the Mempool Accelerator service via its API.

To enhance transparency, acceleration bid boosts are publicly visible on Mempool’s block audit dashboard, highlighted in purple, the firm added. However, accelerations cannot be modified once submitted, and some requests may be canceled without refunds to ensure that the service is not used for “transaction pinning or other types of abuse,” which attempt to manipulate the order of transactions in a block to gain an unfair advantage at the expense of other users.

Accelerator is an alternative to existing on-chain methods

Mempool’s accelerator service offers an alternative to existing on-chain methods to increase the chances of miners including a transaction: replace-by-fee (RBF) and child-pays-for-parent (CPFP).

With RBF, the sender of an unconfirmed transaction creates a new higher fee transaction, spending some of the same inputs, often accepted over the original transaction. However, a new transaction must be signed, the senders’ wallet must support RBF and the transaction ID will change.

With CPFP, the recipient of an unconfirmed transaction spends their unconfirmed transaction output, increasing the effective fee of the original transaction, as a miner can’t include the new transaction without processing the original. However, a new transaction must be signed, the senders’ wallet must support CPFP and limitations mean it is not possible for some transactions.

Alternatively, Mempool Accelerator uses an out-of-band payment rather than a new on-chain bitcoin transaction that needs to be signed. The main drawback is that users are then relying on a centralized third party rather than the trustless peer-to-peer Bitcoin network.

The service charge is also substantially higher than average transaction fees — around 100 times the current average $0.39 fee, The Block found — meaning it is likely only suitable for larger priority transactions. “Your transaction will be prioritized by up to 43.4% of miners. This will reduce your expected waiting time until the first confirmation to within ~9 minutes,” a test of the service stated.

Mempool said users should always use RBF or CPFP if possible, but its accelerator service is useful in scenarios such as where users have limited wallet functionality for transactions, multisig complexities, opening and closing Lightning channels and retaining the same transaction ID, among others.