What is Mempool?

The mempool, short for memory pool, is the holding area for transactions that have been broadcast to the network but not yet added to a block. Validators or miners pick transactions from the mempool, often prioritising those offering higher fees, and include them in the next blocks. It is essentially the network’s pending queue.

This matters because it explains why transactions with low fees can sit unconfirmed during congestion. If you underpay on gas, your transaction may languish in the mempool while higher-paying ones jump ahead.

Example: during a busy mint, thousands of transactions flood the mempool, and yours confirms quickly only if its gas price is competitive; otherwise it waits.

Safety note: the mempool is public, so pending transactions can be seen and even exploited before confirmation, which is how front-running and MEV work. This is also why you can suffer high slippage or sandwich attacks on visible large trades. Be mindful when making big swaps, and use slippage protection. Related terms include gas fee, gwei, MEV, and slippage.