Tools to test out replace-by-fee functionality. You'll need a local node with the replace-by-fee patch. A version applied to Bitcoin Core v0.11.0 is available at https://github.com/petertodd/bitcoin/tree/replace-by-fee-v0.11.0
Requirements: Python3 (python-bitcoinlib included in repo as subtree)
Increases the fee on a transaction by double-spending it with a second transaction paying the original recipients. The change output will have its value reduced to make the fee higher, and there may be additional inputs added if the original inputs weren't enough.
./doublespend.py <address> <amount>
Creates two transactions in succession. The first pays the specified amount to the specified address. The second double-spends that transaction with a transaction with higher fees, paying only the change address. In addition you can optionally specify that the first transaction additional OP-RETURN, multisig, and "blacklisted" address outputs. Some miners won't accept transactions with these output types; those miners will accept the second double-spend transaction, helping you achieve a succesful double-spend.
Incremental Send Many
./sendmany.py <address> <amount>
Finds an unconfirmed transaction in your wallet that has opted into full-RBF and rebroadcasts it with an additional output. If no such transaction exists, a new opt-in full-RBF transaction is created. The first transaction input is kept to ensure a double-spend; all other inputs are re-optimized for the new set of outputs. This can be significantly cheaper than respending unconfirmed outputs in long transaction chains.
Depends on the availability of the fundrawtransaction RPC call, which is currently only available in git master. (will be in Bitcoin Core v0.12.0)
Opt-In Full-RBF pull-req: https://github.com/bitcoin/bitcoin/pull/6871