fundrawtransaction - Bitcoin {diallowed}

Example code for the fundrawtransaction JSON RPC method. Сomplete guide on how to use fundrawtransaction JSON RPC in GetBlock Web3 documentation.

This method adds inputs to a transaction until it has enough value to meet its output value. This will not modify existing inputs, and will add at most one change output to the transaction.

Parameters

Parameter	Type	Required	Description
hexstring	string	Yes	The hex string of the raw transaction.
options	object	No	Options for funding.
options.add_inputs	boolean	No	Include inputs other than watch-only ones (default: true).
options.changeAddress	string	No	The Bitcoin address for receiving change.
options.changePosition	number	No	The index of the change output.
options.conf_target	number	No	Confirmation target in blocks.
options.estimate_mode	string	No	Fee estimation mode: "unset", "economical", "conservative".
options.fee_rate	number	No	Fee rate in sat/vB.
options.includeWatching	boolean	No	Include inputs from watch-only addresses.
options.lockUnspents	boolean	No	Lock selected unspent outputs (default: false).
options.replaceable	boolean	No	Marks transaction as BIP125 replaceable.
options.subtractFeeFromOutputs	array	No	Array of output indexes to subtract fee from.
iswitness	boolean	No	Whether the transaction hex is a serialized witness transaction.

Request

cURL

curl --location --request POST 'https://go.getblock.io/<ACCESS-TOKEN>/' \
--header 'Content-Type: application/json' \
--data-raw '{
    "jsonrpc": "2.0",
    "method": "fundrawtransaction",
    "params": ["0200000001...00000000", {"conf_target": 6, "replaceable": true}],
    "id": "getblock.io"
}'

Axios

Request

Rust

Response

{
    "jsonrpc": "2.0",
    "id": "getblock.io",
    "result": {
        "hex": "0200000002074a0bfaf4462cef0a5665b89fd7fd5e...",
        "fee": 0.00001234,
        "changepos": 1
    }
}

Response Parameters

Field	Type	Description
hex	string	The resulting funded raw transaction hex.
fee	number	Fee in BTC the transaction will pay.
changepos	number	The position of the added change output, or -1 if none.

Use Case

The fundrawtransaction method is essential for:

• Automatically selecting UTXOs for transactions

• Adding change outputs to transactions

• Building transactions with optimal fee rates

• Creating RBF-enabled transactions

• Simplifying transaction construction workflows

• Supporting complex payment scenarios

Error Handling

Status Code	Error Message	Cause
403	Forbidden	Missing or invalid ACCESS-TOKEN.
-4	Insufficient funds	Not enough funds available to fund the transaction.
-22	TX decode failed	The transaction hex is malformed.

Integration Notes

The fundrawtransaction method helps developers:

• Build automated UTXO selection

• Create fee-optimal transactions

• Implement change address management

• Support coin control features

• Build batch payment systems