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Pending Transactions

Pending transactions are transactions that have been submitted but not yet included in a block. They sit in the node's mempool (transaction pool) waiting for a validator to pick them up. Monitoring them is useful for transaction tracking dashboards, detecting when your own transactions are waiting, and MEV analysis. MEV (Maximal Extractable Value) bots monitor pending transactions to find profitable opportunities like arbitrage.

Ethereum provides two ways to access pending transactions: querying the pending block, or creating a filter that returns new pending transaction hashes.

dotnet add package Nethereum.Web3

Get Pending Transactions from the Pending Block​

Use BlockParameter.CreatePending() to query the pending block and retrieve all its transactions:

using Nethereum.Web3;
using Nethereum.RPC.Eth.DTOs;

var web3 = new Web3("https://mainnet.infura.io/v3/YOUR-PROJECT-ID");

var block = await web3.Eth.Blocks.GetBlockWithTransactionsByNumber
    .SendRequestAsync(BlockParameter.CreatePending());

Console.WriteLine("Pending transactions:");
foreach (var txn in block.Transactions)
{
    Console.WriteLine(
        $"Hash:{txn.TransactionHash}, From: {txn.From}, To: {txn.To}, " +
        $"Value: {txn.Value}, Nonce: {txn.Nonce}, Data: {txn.Input}");
}

The Input field contains ABI-encoded function call data — see Decode Transactions to parse it.

Get Pending Transaction Hashes Using Filters​

Filters let you poll for new pending transactions since your last check, rather than fetching all pending state each time. Create a pending transaction filter and poll for new entries:

var web3 = new Web3("http://localhost:8545");

var pendingFilter = await web3.Eth.Filters.NewPendingTransactionFilter
    .SendRequestAsync();

var filterChanges = await web3.Eth.Filters.GetFilterChangesForBlockOrTransaction
    .SendRequestAsync(pendingFilter);

foreach (var txnHash in filterChanges)
{
    Console.WriteLine(txnHash);
}
note

Pending transaction filters are not available on all public nodes. Infura, for example, does not support them. Use a local node or a dedicated node provider for filter-based pending transaction retrieval.

Next Steps​