All terms
The waiting room where broadcast transactions sit before being included in a block.
When you send a transaction it does not go straight into a block. It sits in the mempool, a public queue that every node maintains, until a validator picks it up. Validators generally choose the most profitable transactions first.
Because the mempool is public, anyone can see your pending transaction before it executes. That visibility is what makes front running and sandwich attacks possible.
If your transaction is stuck, it is sitting in the mempool with a fee too low to be attractive. You can usually replace it with a higher fee version.
That a transaction sitting in the mempool is private. It is broadcast to the entire network and visible to anyone watching, including bots that will trade ahead of it. The mempool is a public queue, not a waiting room with a closed door.
Common questions
Can other people see my transaction in the mempool?
How long does a transaction stay in the mempool?
Where this comes up on the site
The guides that actually use this word, rather than a list of everything we have written.
Where to go next
More foundations terms
Want this explained out loud?
Some of these land faster in conversation than in writing. Sessions are one to one and you can ask anything, including the things that feel too obvious to ask.