PSBT (Partially Signed Transaction)

A PSBT, or partially signed Bitcoin transaction, is a standard format for a transaction that has been built but not yet fully signed, so that it can be passed between devices and programs that each hold only part of what is needed. It was specified as BIP-174 to give wallets a common language: a watch-only wallet builds the transaction, an offline or hardware device adds a signature, and a third program broadcasts the finished result. This is what makes air-gapped and multisig workflows practical, because each signer can add a signature independently and the file carries the context — the inputs, their amounts, the derivation information — that a signing device needs in order to show you what you are approving. A PSBT contains no private keys, so it is not secret the way a recovery phrase is. It can still be altered in transit, which is why the amount and destination should be checked on the signing device rather than on the machine that produced the file. Other chains have equivalent formats under other names.