Mempool
The pool of pending transactions broadcast to the network but not yet included in a block.
When a user signs a transaction and submits it, the transaction is broadcast peer-to-peer across the network and lands in each node's mempool. Validators (in PoS) or miners (in PoW) select transactions from the mempool when building the next block, typically prioritizing by fee paid.
The mempool is publicly observable on most chains. Anyone can connect a node and watch incoming transactions before they're confirmed — which is what enables MEV searchers to spot arbitrage and sandwich opportunities. Privacy-preserving mempools (Flashbots Protect on Ethereum) hide your transaction from public observation until inclusion.
Mempool depth indicates network congestion. A deep mempool (many pending tx) means inclusion will be delayed unless you bid up the fee. A shallow mempool means the next block has spare capacity. Tools like mempool.space (Bitcoin) and txstreet show the mempool state in real time.
Mempool dynamics control how quickly your transaction lands and how much you'll pay in gas. Understanding it lets you time low-priority sends for cheap fees.
How CryptoRadar24 tracks it
CryptoRadar24 references mempool conditions when reporting on network demand spikes and gas-price events.
Related terms
FAQ
Is the mempool public?
On most public chains, yes — anyone running a node can see pending transactions. This visibility enables both legitimate fee estimation and MEV extraction.
How long does a transaction stay in the mempool?
Until it's included or evicted. Most nodes drop low-fee transactions after ~3 hours. Re-broadcasting with a higher fee usually clears stuck transactions.
Why is my transaction stuck?
Either the fee is too low for current congestion, or it depends on a previous transaction that hasn't cleared. "Replace by fee" (RBF on Bitcoin, speed-up on Ethereum) lets you re-submit with a higher fee.
Do all chains have a mempool?
Almost all do. Solana doesn't have a traditional mempool — transactions go straight to the leader. Some L2s (Arbitrum, Optimism) have private sequencer mempools where the operator orders transactions before posting them to L1.