One payment, end to end

1. Wallet and signature

A wallet holds keys, not coins. To pay, it builds the payment and signs it with the private key; the signature proves the owner agreed, and it covers the exact amounts and addresses, so nothing can be edited on the way. Safe start covers handling keys without losing them.

2. Inputs and outputs

A payment spends earlier outputs and creates new ones: what you send, and your change back. There is no account balance anywhere in the system; there are only unspent outputs, each locked to an address. The glossary keeps the words straight.

3. The UTXO set

Every node keeps the full set of unspent outputs, the UTXO set, and checks a payment against it: are these outputs real, unspent, and signed for? That check is what stops the same coin being spent twice at the door.

4. Mass and fee

Each payment has a mass, a size-like weight the network charges for; a simple payment is about 2,000 mass units. The fee is what the sender offers the miners to carry it. The fee material in Check it yourself reads today's price for that mass off the live network.

5. Into a block

Miners gather waiting payments into blocks, about ten blocks a second. Inclusion is the first milestone: the payment is now inside a block, in public, timestamped by the block itself. Fullness today is low; the strip on the home panel counts the last 100 blocks.

6. Ordering

Blocks arrive as a web, not a chain, so the network computes one agreed order over all of them. If two payments conflict, the one earlier in that order stands and the later one is refused. One order walks the computation, and its block card shows one block's fields, pay and view.

7. Blue depth

After inclusion, newer blue blocks pile on top. Depth is counted in blue score, and the practical range on this site is about 1 to 3 seconds of burial before a payment carries Bitcoin-hour weight. The receipt below counts a real payment's depth as it grows.

8. Safe to spend

The receiver can treat the payment as theirs once its depth matches the size of the payment: small amounts at a few blue blocks, large ones deeper. Nothing here is instant or absolute; certainty is a slope, and the certainty calculator in Price and risk puts numbers on it.