diff --git a/src/ZB.MOM.WW.ScadaBridge.DelmiaNotifier/DiagLog.cs b/src/ZB.MOM.WW.ScadaBridge.DelmiaNotifier/DiagLog.cs
new file mode 100644
index 00000000..f2b3a9de
--- /dev/null
+++ b/src/ZB.MOM.WW.ScadaBridge.DelmiaNotifier/DiagLog.cs
@@ -0,0 +1,39 @@
+using System.Globalization;
+
+namespace ZB.MOM.WW.ScadaBridge.DelmiaNotifier;
+
+/// <summary>
+/// Best-effort diagnostics: writes UTC-timestamped lines to stderr and, when a log path is configured,
+/// appends them to a file (relative to the exe). Never throws — diagnostics must not break the YES/NO path.
+/// </summary>
+internal sealed class DiagLog(string? logPath)
+{
+    private readonly string? _logPath = string.IsNullOrWhiteSpace(logPath) ? null : logPath;
+
+    public void Write(string message)
+    {
+        var line = string.Create(CultureInfo.InvariantCulture, $"{DateTime.UtcNow:yyyy-MM-ddTHH:mm:ss.fffZ} {message}");
+        Console.Error.WriteLine(line);
+
+        if (_logPath is null)
+        {
+            return;
+        }
+
+        try
+        {
+            var fullPath = Path.IsPathRooted(_logPath) ? _logPath : Path.Combine(AppContext.BaseDirectory, _logPath);
+            var dir = Path.GetDirectoryName(fullPath);
+            if (!string.IsNullOrEmpty(dir))
+            {
+                Directory.CreateDirectory(dir);
+            }
+
+            File.AppendAllText(fullPath, line + Environment.NewLine);
+        }
+        catch
+        {
+            // diagnostics are best-effort; swallow file errors so the YES/NO contract is unaffected
+        }
+    }
+}
diff --git a/src/ZB.MOM.WW.ScadaBridge.DelmiaNotifier/Program.cs b/src/ZB.MOM.WW.ScadaBridge.DelmiaNotifier/Program.cs
index 7d6959e6..28a458eb 100644
--- a/src/ZB.MOM.WW.ScadaBridge.DelmiaNotifier/Program.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.DelmiaNotifier/Program.cs
@@ -2,5 +2,72 @@ namespace ZB.MOM.WW.ScadaBridge.DelmiaNotifier;
 
 internal static class Program
 {
-    public static int Main(string[] args) => 0; // replaced in Task 7
+    public static async Task<int> Main(string[] args)
+    {
+        var stdout = Console.Out;
+
+        // Config first, so the diagnostic log can honour the configured LogPath even for early failures.
+        NotifierConfig cfg;
+        try
+        {
+            cfg = ConfigLoader.LoadFromDefaultFile();
+        }
+        catch (Exception ex)
+        {
+            new DiagLog(null).Write("config load failed: " + ex.Message);
+            return Reporter.Report(false, "config load failed: " + ex.Message, stdout);
+        }
+
+        var log = new DiagLog(cfg.ScadaBridge.LogPath);
+
+        try
+        {
+            var parse = ArgParser.Parse(args);
+            if (!parse.Ok)
+            {
+                log.Write("arg error: " + parse.Error);
+                return Reporter.Report(false, parse.Error!, stdout);
+            }
+
+            var baseUrls = ConfigLoader.SplitBaseUrls(cfg.ScadaBridge.BaseUrls);
+            if (baseUrls.Length == 0)
+            {
+                log.Write("no BaseUrls configured");
+                return Reporter.Report(false, "no BaseUrls configured", stdout);
+            }
+
+            var apiKey = ConfigLoader.ResolveApiKey(Environment.GetEnvironmentVariable);
+            if (apiKey is null)
+            {
+                log.Write("API key not configured (SCADABRIDGE_API_KEY)");
+                return Reporter.Report(false, "API key not configured (SCADABRIDGE_API_KEY)", stdout);
+            }
+
+            using var http = new HttpClient { Timeout = TimeSpan.FromSeconds(cfg.ScadaBridge.TimeoutSeconds) };
+            var sender = new LoggingRecipeSender(new HttpRecipeSender(http, apiKey), log);
+
+            log.Write($"notifying {baseUrls.Length} URL(s) for machine {parse.Payload!.MachineCode}");
+            var result = await Notifier.RunAsync(baseUrls, parse.Payload, sender, CancellationToken.None);
+            log.Write($"result: ok={result.Ok} reason={result.Reason}");
+            return Reporter.Report(result.Ok, result.Reason, stdout);
+        }
+        catch (Exception ex)
+        {
+            log.Write("unexpected error: " + ex);
+            return Reporter.Report(false, "unexpected error: " + ex.Message, stdout);
+        }
+    }
+
+    /// <summary>Decorates a sender to emit a per-attempt diagnostic line; keeps stdout reserved for the YES/NO contract.</summary>
+    private sealed class LoggingRecipeSender(IRecipeSender inner, DiagLog log) : IRecipeSender
+    {
+        public async Task<AttemptOutcome> SendAsync(string baseUrl, RecipeDownload payload, CancellationToken ct)
+        {
+            var outcome = await inner.SendAsync(baseUrl, payload, ct);
+            log.Write(outcome.Kind == AttemptKind.ConnectFailed
+                ? $"attempt {baseUrl}: connect failed: {outcome.Error}"
+                : $"attempt {baseUrl}: HTTP {outcome.StatusCode}");
+            return outcome;
+        }
+    }
 }
diff --git a/src/ZB.MOM.WW.ScadaBridge.DelmiaNotifier/Reporter.cs b/src/ZB.MOM.WW.ScadaBridge.DelmiaNotifier/Reporter.cs
new file mode 100644
index 00000000..e8419785
--- /dev/null
+++ b/src/ZB.MOM.WW.ScadaBridge.DelmiaNotifier/Reporter.cs
@@ -0,0 +1,22 @@
+namespace ZB.MOM.WW.ScadaBridge.DelmiaNotifier;
+
+/// <summary>
+/// Maps an outcome to the legacy WWNotifier stdout contract: <c>YES</c> + exit 0 on success,
+/// <c>NO</c> followed by a reason line + exit -1 on failure. The writer is injected so stdout is the
+/// only thing Delmia ever parses (LF-terminated, deterministic across platforms).
+/// </summary>
+internal static class Reporter
+{
+    public static int Report(bool ok, string reason, TextWriter stdout)
+    {
+        if (ok)
+        {
+            stdout.Write("YES\n");
+            return 0;
+        }
+
+        stdout.Write("NO\n");
+        stdout.Write(reason);
+        return -1;
+    }
+}
diff --git a/tests/ZB.MOM.WW.ScadaBridge.DelmiaNotifier.Tests/ReporterTests.cs b/tests/ZB.MOM.WW.ScadaBridge.DelmiaNotifier.Tests/ReporterTests.cs
new file mode 100644
index 00000000..88c65ce7
--- /dev/null
+++ b/tests/ZB.MOM.WW.ScadaBridge.DelmiaNotifier.Tests/ReporterTests.cs
@@ -0,0 +1,24 @@
+using ZB.MOM.WW.ScadaBridge.DelmiaNotifier;
+
+namespace ZB.MOM.WW.ScadaBridge.DelmiaNotifier.Tests;
+
+public class ReporterTests
+{
+    [Fact]
+    public void Success_writes_YES_and_returns_0()
+    {
+        using var sw = new StringWriter();
+        var code = Reporter.Report(true, "", sw);
+        Assert.Equal("YES\n", sw.ToString());
+        Assert.Equal(0, code);
+    }
+
+    [Fact]
+    public void Failure_writes_NO_then_reason_and_returns_minus1()
+    {
+        using var sw = new StringWriter();
+        var code = Reporter.Report(false, "boom", sw);
+        Assert.Equal("NO\nboom", sw.ToString());
+        Assert.Equal(-1, code);
+    }
+}