Coin Smith
Bitcoin PSBT Transaction Builder. Select coins, compute fees, build unsigned transactions.
Fixture Input
Quick Load
How It Works
- UTXOs
- Unspent outputs your wallet controls — like bills in a physical wallet.
- Coin Selection
- Picks which UTXOs to spend. Greedy strategy (largest first) minimises input count.
- Fee
- Paid to miners. Larger transactions cost more. Fee = fee_rate × vbytes.
- Change
- Leftover sent back to yourself. If below 546 sats (dust), absorbed into the fee.
- PSBT
- Partially Signed Bitcoin Transaction — unsigned, bundled with metadata for hardware signers.
- RBF
- Replace-By-Fee — allows bumping the fee later. Signalled via nSequence <= 0xFFFFFFFD.
- Locktime
- Prevents mining before a given block height or Unix timestamp.