testmempoolaccept - Bitcoin

Example code for the testmempoolaccept JSON-RPC method. Complete guide on how to use testmempoolaccept JSON-RPC in GetBlock Web3 documentation.

This method tests whether raw transactions can be accepted into the mempool without actually submitting them to the network.

Parameters

Parameter	Type	Required	Description
rawtxs	array	Yes	Array of hex strings of raw transactions.
maxfeerate	number/string	No	Reject transactions whose fee rate is higher than this (default: 0.10 BTC/kvB).

Request

cURL

curl --location --request POST 'https://go.getblock.io/<ACCESS-TOKEN>/' \
--header 'Content-Type: application/json' \
--data-raw '{
    "jsonrpc": "2.0",
    "method": "testmempoolaccept",
    "params": [["0200000001074a0bfaf4462cef0a5665b89fd7fd5e4f8536630cde6824d09b20400b2f65ee000000006a47304402...00000000"]],
    "id": "getblock.io"
}'

Axios

Request

Rust

Response

Accepted

{
    "id": "getblock.io",
    "result": [
        {
            "txid": "52273e0ce6cf3452932cfbc1c517c0ce1af1d255fda67a6e3bd63ba1d908c8c2",
            "wtxid": "abc123def456789...",
            "allowed": true,
            "vsize": 141,
            "fees": {
                "base": 0.00001410
            }
        }
    ]
}

Rejected

Response Parameters

Field	Type	Description
txid	string	The transaction hash.
wtxid	string	The witness transaction hash (if accepted).
allowed	boolean	Whether the transaction would be accepted.
vsize	number	Virtual transaction size (if accepted).
fees	object	Transaction fees (if accepted).
fees.base	number	Transaction fee in BTC.
reject-reason	string	Rejection reason (if not accepted).

Use Case

The testmempoolaccept method is essential for:

• Validating transactions before broadcast

• Testing transaction construction

• Pre-flight checks for payment systems

• Fee validation and adjustment

• Transaction debugging

• Batch transaction validation

Error Handling

Status Code	Error Message	Cause
403	Forbidden	Missing or invalid ACCESS-TOKEN.
-32602	Invalid params	Missing or invalid rawtxs array.
-26	Transaction rejected	Transaction failed validation (see reject-reason).
-22	TX decode failed	Invalid raw transaction hex.

Common Rejection Reasons

Reason	Description
insufficient fee	Fee is below minimum required.
txn-mempool-conflict	Conflicts with transaction in mempool.
bad-txns-inputs-missingorspent	Input transaction not found or already spent.
non-final	Transaction is not final (locktime).
absurdly-high-fee	Fee exceeds maxfeerate.

Integration With Web3

The testmempoolaccept method helps developers:

• Validate transactions before broadcasting

• Build transaction preview features

• Implement fee adequacy checks

• Debug transaction construction issues

• Create safe transaction submission workflows