transaction-scheduler

Schedule future Bitcoin transactions by leveraging nLockTime.

Use cases

Dead man's switch

A user could sign a transaction with a timelock that sends their cold storage funds to a trusted third party if they lose access to their keys. If the user retains access to their keys, they can spend the inputs and invalidate the timelocked transaction. These transactions should be RBF and multiple transactions should be created with different fees if the acceptable fees change drastically. If unsuccessful, this service can broadcast the transaction again at a future date if it drops out of the mempool. Users can also specify that they only want to broadcast the transaction if it has an acceptable fee set, and the service will only broadcast the transaction if the fee is appropriate.

Scheduled payments

Let's say you want to schedule payments to a service provider or a dependant. You could sign transactions with a future date as the timelock and send them to this service. The transaction would then be broadcast at a future date.

Fees

The network fees may be high, and you have a non-urgent payment to make. You could sign a transaction or multiple transactions with different timelocks to be attempted. These transactions can be RBF enabled, allowing you to replace old transaction(s) stuck in the mempool. This could look like the following:

1. Sign five RBF transactions with different timelocks, in ascending order from the lowest fee to the highest fee
2. If the first transaction is still in the mempool at the time of the second timelock, broadcast the second one to replace the first
3. Hopefully, one of the timelocked transactions ends up in the mempool.

Users can also specify that they only want to broadcast the transaction if it has an acceptable fee set, and the service will only broadcast the transaction if the fee is appropriate.

Automatically resetting 2FA multisig CSV transactions

Blockstream green supports 2FA multisig, a service that requires you provide a valid 2FA code for blockstream to co-sign your transactions. Blockstream green uses CSV transactions that enable you to spend the funds with your single key after a certain time has been reached. This is useful for those who have lost their 2FA method, or in the event that blockstream's server goes down.

Users of this feature need to ensure that they send new transactions to reset the timelock. Failure to do so will mean that the security of their funds will revert to a single sig wallet.

Users of the blockstream green service can have their CSV reset automatically by signing a transaction with a future timelock, and posting it to this service. This service will then broadcast their new transaction, enabling them to reset their timelock without having to go back to their wallet.

Users can add a grace period to this timelock, enabling them to spend their funds once the original CSV becomes valid, and before the future transaction is set to become valid.

UTXO consolidation when fees are low

It is considered good practice to consolidate UTXOs when fees are low, as this enables you to reduce the fee of subsequent transactions. A user can sign a consolidation transaction with a low fee, and have it be broadcast when fees drop.

API

POST /schedule/tx

Body:

{
  "rawTx": "YOUR_RAW_SIGNED_TRANSACTION_IN_HEX",
  "checkFee": "boolean"
}

Params:

rawTx: your raw transaction bytes as hex. checkFee: set to true if you want to prevent broadcasting a transaction if it has a fee that is lower than the recommendation, otherwise false.

Successful output:

{
  "body": true,
  "status": 200
}