Bridging .NET and Web3: Building Blockchain Applications with Nethereum

Introduction

Blockchain is no longer just hype it’s a foundational technology powering decentralized finance (DeFi), NFTs, and next-gen applications. Among blockchain platforms, Ethereum stands out because of its ability to run smart contracts.

For .NET developers, the good news is that you don’t need to switch ecosystems. With Nethereum, you can interact with Ethereum directly from your C# applications. This article introduces how to integrate Ethereum into a .NET application using Nethereum. It walks through the basics of connecting to the blockchain, retrieving wallet balances, and sending transactions. Designed for .NET developers, it shows how to work with Web3 using familiar C# tools and patterns. The guide also includes a ready-to-use Visual Studio solution to help you get started quickly.

In this article, you’ll learn:

How Ethereum works (quick overview)
How to set up a .NET project
How to connect to Ethereum blockchain
How to send transactions
How to interact with smart contracts
A complete demonstration with code samples

What is Ethereum?

Ethereum is a decentralized platform that allows developers to build applications using smart contracts: self-executing programs stored on the blockchain.

Key components:

ETH → Native cryptocurrency
Smart Contracts → Business logic
Wallets → Store private keys
Nodes → Connect to the blockchain

What is Nethereum?

Nethereum is a .NET integration library that allows you to:

Connect to Ethereum nodes
Send transactions
Deploy and interact with smart contracts
Build blockchain-powered APIs

Prerequisites

Before starting, we will need followings:

.NET 8 SDK installed
Basic knowledge of C#
Ethereum wallet (e.g., MetaMask)
Free RPC endpoint from Infura or Alchemy

Step 1: Create Project

dotnet new webapi -n EthereumDemo
cd EthereumDemo

Install Nethereum:

dotnet add package Nethereum.Web3

Step 2: Connect to Ethereum Network

sample code example to get the block number.

using Nethereum.Web3;
var web3 = new Web3("https://mainnet.infura.io/v3/YOUR_INFURA_KEY");
var blockNumber = await web3.Eth.Blocks.GetBlockNumber.SendRequestAsync();
Console.WriteLine($"Current Block: {blockNumber.Value}");

Step 3: Send Ethereum Transaction

using Nethereum.Web3;
using Nethereum.Web3.Accounts;

var account = new Account("YOUR_PRIVATE_KEY");
var web3 = new Web3(account, "https://sepolia.infura.io/v3/YOUR_INFURA_KEY");

var transaction = await web3.Eth.GetEtherTransferService()
    .TransferEtherAndWaitForReceiptAsync(
        "RECEIVER_ADDRESS",
        0.01m);

Console.WriteLine($"Transaction Hash: {transaction.TransactionHash}");

Step 4: Interact with Smart Contract

Example: Reading a value from a contract that is deployed in the ethereum blockchain.

var web3 = new Web3("https://sepolia.infura.io/v3/YOUR_INFURA_KEY");

string contractAddress = "YOUR_CONTRACT_ADDRESS";

var contract = web3.Eth.GetContract(ABI, contractAddress);
var function = contract.GetFunction("getValue");

var result = await function.CallAsync<int>();
Console.WriteLine(result);

Step 5: API Controller


using Microsoft.AspNetCore.Mvc;
using Nethereum.Web3;
using Nethereum.Web3.Accounts;

namespace EthereumDemo.Controllers;

[ApiController]
[Route("api/[controller]")]
public class WalletController : ControllerBase
{
    private readonly string rpcUrl = "https://sepolia.infura.io/v3/YOUR_INFURA_KEY";

    [HttpGet("balance/{address}")]
    public async Task<IActionResult> GetBalance(string address)
    {
        var web3 = new Web3(rpcUrl);
        var balance = await web3.Eth.GetBalance.SendRequestAsync(address);
        var ether = Web3.Convert.FromWei(balance.Value);
        return Ok(ether);
    }

    [HttpPost("send")]
    public async Task<IActionResult> Send(string privateKey, string toAddress, decimal amount)
    {
        var account = new Account(privateKey);
        var web3 = new Web3(account, rpcUrl);

        var receipt = await web3.Eth.GetEtherTransferService()
            .TransferEtherAndWaitForReceiptAsync(toAddress, amount);

        return Ok(receipt.TransactionHash);
    }
}

Conclusion

Ethereum opens up a new paradigm of decentralized application development, and with Nethereum, .NET developers can seamlessly integrate blockchain into their existing systems. Whether you’re building fintech apps or experimenting with Web3, the combination of Ethereum + .NET is powerful and future-ready.

This article showed how to integrate Ethereum into a .NET app using Nethereum, covering connection, balance checks, and transactions. It demonstrates how .NET developers can work with blockchain using familiar tools. The provided Visual Studio solution gives a solid starting point for real-world Web3 applications.

For begineers I would recommend to start small connect to the blockchain, read some data, and gradually move toward smart contracts and decentralized applications.

Sample code can be found here.