Bitcoin Core bumpfee RPC: BIP 125 Replacement Guide

This guide explains Bitcoin Core bumpfee RPC in plain English. It shows what the command does, what its result means and what it cannot prove.

Eligibility checks

The txid must identify an in-wallet opt-in RBF transaction. It must remain unconfirmed, and neither wallet nor mempool may contain a transaction spending one of its outputs. Verify mempool membership, confirmation status, replaceability and descendants immediately before the call. A state change between check and submission can still produce a controlled failure.

Fee source and units

The historical options allowed confTarget, totalFee and estimate_mode values UNSET, ECONOMICAL or CONSERVATIVE. TotalFee is an absolute fee in satoshis, not a rate. If using estimation or settxfee, record the effective mode, target, estimated rate and transaction virtual size. Reject values that confuse BTC, satoshis and satoshis per virtual byte.

Change-output funding

Core reduced or removed change to pay the increase and did not add new inputs when change was too small. Near dust, the actual fee could be slightly higher than totalFee because the change output disappeared. Decode old and new transactions, confirm every external destination and amount is identical, then account for the exact change and fee difference.

Replacement signalling

replaceable true retained original sequence numbers, while false raised eligible sequence values to stop explicit signalling. A transaction could remain replaceable in practice through an unconfirmed replaceable ancestor. Do not promise finality based only on the option; inspect the entire unconfirmed ancestry and continue monitoring conflicts.

Relay floor and policy

The replacement needed at least enough extra fee rate to satisfy the node’s incremental relay fee and broader BIP 125 policy. Peers and miners may have different mempool policy. Successful local acceptance is not confirmation or universal relay. Observe several peers, explorer-independent nodes and eventual chain inclusion before closing the incident.

Result and accounting

Record replacement txid, origfee, fee and every returned error. Link both txids to one logical payment so customer systems do not create a second order or withdrawal. Continue watching the original, replacement and any conflict through enough confirmations, including after a reorganisation.

How specialists test it

Operators test the command on a non-production node first. They check a normal reply, an invalid request, a timeout and a restart. This shows what the response means and prevents one local result from being mistaken for a network-wide outcome.

Conclusion

bumpfee can rescue an eligible wallet payment, but it is a stateful replacement rather than a simple fee edit. Safe operation preserves recipient outputs, uses exact fee units and monitors both transactions through final resolution.