What Is Mempool?
The mempool (memory pool) is the waiting area for unconfirmed transactions. When you submit a transaction, it enters the mempool where it waits until a miner or validator includes it in a block. Each node maintains its own mempool, so the global mempool is a collection of all nodes' pending transaction pools.
How Mempool Works
Transactions in the mempool are prioritized by fee: higher-fee transactions get included in blocks first. During periods of high demand, the mempool grows (more transactions waiting), fees increase (users bid for priority), and lower-fee transactions can wait hours or days. Mempool size and average fee levels are real-time indicators of network congestion.
Why It Matters for Traders
The mempool is where MEV bots operate — scanning pending transactions for profitable opportunities (front-running, sandwich attacks, liquidations) and submitting their own transactions with higher fees to get ahead. For traders, mempool monitoring reveals: pending large transactions that might move markets, DEX swap activity before it's confirmed, and network congestion that might delay your own transactions.
