Bitcoin address
The string of letters and numbers someone needs to send you bitcoin. It's made from a public key or a script, and its first characters tell you its format.
An address isn’t an account, and it doesn’t hold a balance. It describes the condition for spending whatever is sent to it, usually a signature from one key, or from several. Your wallet makes a new one whenever you ask, and the usual advice is to use each one only once, since anyone can look up an address and see every payment made to it.
Its first characters tell you the format:
- 1: the original format, made from a single public key.
- 3: made from a script, often a multisig wallet’s, under BIP13, from 2011.
- bc1q: SegWit, under BIP173, from 2017.
- bc1p: Taproot, under BIP350, from 2020, in use since November 2021.
Addresses that begin with bc1 use only lowercase letters and digits, so they’re easier to read out and copy, and a checksum that, according to BIP173, is guaranteed to catch any mistake in up to four characters. That checksum had a gap: in an address ending in “p”, extra “q” characters could be slipped in or taken out just before it without being caught. BIP350 fixed it with a corrected version, Bech32m, which Taproot addresses use.
Before you send
A checksum catches typos, not a valid address that’s the wrong one. Paste the address rather than type it, check all of it rather than its first and last characters, and send a small amount first to an address you haven’t used before: a bitcoin payment can’t be reversed. Address poisoning is one way people end up sending to the wrong one.