Scan Bitcoin blocks, looking for OP_RETURN outputs containing text. Requires a synced fullnode and the NBitcoin library

OpReturn.cs

using NBitcoin;
using NBitcoin.RPC;
using System;
using System.IO;
using System.Linq;
using System.Text;


class OpReturnScan
{
    /// <summary>
    /// Insert path to your full-node auth cookie file
    /// </summary>
    const string CookieFile = "";

    /// <summary>
    /// Begin scan at this block
    /// </summary>
    const int Start = 630_000 - 2;

    /// <summary>
    /// End scan at this block
    /// </summary>
    const int End = 630_000 + 2;


    static RPCClient InitBitcoinRpc()
    {
        var credentials = RPCCredentialString.Parse(File.ReadAllText(CookieFile));
        var rpc = new RPCClient(credentials, Network.Main);

        return rpc;
    }

    public static void Main(string[] args)
    {
        var rpc = InitBitcoinRpc();

        for (int i = Start; i <= End; i++)
        {
            var blk = rpc.GetBlock(i);

            foreach (var tx in blk.Transactions)
            {
                foreach (var vout in tx.Outputs)
                {
                    var ops = vout.ScriptPubKey.ToOps().ToArray();

                    // Detect if the TXO script follows the format "OP_RETURN {data}"
                    if (ops.Length >= 2 &&
                       ops[0].Code == OpcodeType.OP_RETURN &&
                       ops[1].PushData?.Length > 0)
                    {
                        var text = Encoding.UTF8.GetString(ops[1].PushData);

                        // Discard op_return's about Omni and RSK because there's a lot of them
                        if (!text.StartsWith("omni") && !text.StartsWith("RSKBLOCK"))
                        {
                            Console.WriteLine($"{i}:{tx.GetHash()}: \"{text}\"");
                        }
                    }
                }
            }
        }
    }

}