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 checks whether one or more raw transactions would be accepted into the mempool, without broadcasting them. It is used to validate a transaction before sending it.

Parameters

Parameter	Type	Required	Description
rawtxs	array	Yes	Raw transactions as hex strings (currently one at a time)
maxfeerate	number or string	No	Reject if the fee rate exceeds this value (default: 0.10 BTC/kvB)

Request

cURL

curl --location --request POST 'https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/' \
--header 'Content-Type: application/json' \
--data-raw '{
    "jsonrpc": "2.0",
    "method": "testmempoolaccept",
    "params": [["0200000001a1b2c3d4e5f6...0000000000"]],
    "id": "getblock.io"
}'

bitcoinjs-lib

example.js

const axios = require('axios');

const response = await axios.post('https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/', {
    jsonrpc: '2.0',
    method: 'testmempoolaccept',
    params: [["0200000001a1b2c3d4e5f6...0000000000"]],
    id: 'getblock.io'
}, {
    headers: { 'Content-Type': 'application/json' }
});

console.log(response.data.result);

Request

example.py

import requests

response = requests.post(
    'https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/',
    headers={'Content-Type': 'application/json'},
    json={
        'jsonrpc': '2.0',
        'method': 'testmempoolaccept',
        'params': [["0200000001a1b2c3d4e5f6...0000000000"]],
        'id': 'getblock.io'
    }
)

print(response.json())

Rust

example.rs

use reqwest::Client;
use serde_json::{json, Value};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = Client::new();

    let response = client
        .post("https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/")
        .header("Content-Type", "application/json")
        .json(&json!({
            "jsonrpc": "2.0",
            "method": "testmempoolaccept",
            "params": [["0200000001a1b2c3d4e5f6...0000000000"]],
            "id": "getblock.io"
        }))
        .send()
        .await?
        .json::<Value>()
        .await?;

    println!("Result: {}", response["result"]);
    Ok(())
}

Response

{
    "jsonrpc": "2.0",
    "id": "getblock.io",
    "result": [
        {
            "txid": "4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b",
            "wtxid": "4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b",
            "allowed": true,
            "vsize": 141,
            "fees": {
                "base": 2.82e-05,
                "effective-feerate": 0.0002,
                "effective-includes": [
                    "4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b"
                ]
            }
        }
    ]
}

Response Parameters

Parameter	Type	Description
jsonrpc	string	JSON-RPC protocol version ("2.0")
id	string	Request identifier matching the request
result	array	Array with one acceptance result per transaction

Array Item

Field	Type	Description
txid	string	The transaction ID
allowed	boolean	Whether the transaction would be accepted
vsize	number	Virtual size if allowed
reject-reason	string	Reason for rejection, present when not allowed

Use Cases

• Pre-Flight Checks: Validate a transaction before broadcasting

• Fee Validation: Confirm the fee rate is acceptable

• Wallet UX: Warn users of likely rejection

• Automation: Gate broadcasts on acceptance

Error Handling

Error Code	Message	Description
403	Forbidden	Missing or invalid ACCESS-TOKEN
-8	Invalid parameter	A parameter is out of range or malformed
-32601	Method not found	The method is not available on this endpoint
-32602	Invalid params	A parameter is missing or has the wrong type