What is the mempool?

When a wallet sends a transaction it does not go into a block straight away. It is broadcast to full nodes, each of which validates it and puts it in its mempool: the waiting room of spends that are valid but not yet confirmed. The next farmer to win a transaction block fills it from that room. This site is a window onto the mempool of the node it reads from.

Spend bundles, not transactions

What waits in the mempool is a spend bundle: a set of coin spends plus one aggregated signature. A simple payment spends one or two coins and creates two (the payment and the change); an offer being taken or a token swap can spend dozens. Its id is the hash of the bundle, and that is what you paste into search to follow it.

How a block gets filled

A block has room for 11 billion units of cost, and each bundle uses some of it. The node sorts waiting bundles by fee per cost (mojos per unit of cost), takes the best-paying ones first, and stops when the block is full. The dashboard's next block view runs the same packing on the live mempool so you can see roughly which block your spend will land in and watch the block fill up as bundles arrive.

Fees

Most of the time the mempool is not full, and zero-fee spends confirm within a few blocks. Fees start to matter in two situations: when the mempool holds more than the node's limit (ten blocks worth of cost) so that only paying spends are accepted, and when more bundles wait than the next block can carry. The fees page shows the node's own estimate for reaching a block within one, five or ten minutes and what a typical transfer costs at that rate.

Leaving the mempool

A bundle leaves the mempool when a block includes it (confirmed), when one of its coins gets spent by another bundle first, or when the node drops it after a reorg or because it is no longer valid (removed). A transaction page keeps showing a removed bundle's coins when Coinset recorded it; nodes themselves forget dropped bundles.

Reading the graphs

• Cost used is how much of the mempool's capacity is taken, split by fee band.
• Incoming is bundles per minute as seen by this browser.
• Projected blocks group the queue into blocks in the order the node would pick them.