diff --git a/SVSim.BattleNode/Bridge/BattleNodeOptions.cs b/SVSim.BattleNode/Bridge/BattleNodeOptions.cs
index 1cd35971..b9f7d374 100644
--- a/SVSim.BattleNode/Bridge/BattleNodeOptions.cs
+++ b/SVSim.BattleNode/Bridge/BattleNodeOptions.cs
@@ -1,13 +1,25 @@
 namespace SVSim.BattleNode.Bridge;
 
 /// <summary>
-/// DI-injected options for the battle node. NodeServerUrl matches the prod
-/// do_matching wire format: <c>host:port/socket.io/</c>, no scheme prefix.
-/// BestHTTP's SocketManager parses it as the Socket.IO v2 endpoint URL.
+/// DI-injected options for the battle node.
 /// </summary>
 public sealed class BattleNodeOptions
 {
-    public string NodeServerUrl { get; set; } = "localhost:5148/socket.io/";
+    /// <summary>
+    /// The Socket.IO v2 endpoint URL echoed back to the client on <c>/*/do_matching</c>
+    /// success (matching_state 3004/3007/3011). Matches the prod do_matching wire format:
+    /// <c>host[:port]/socket.io/</c> — no scheme prefix, must end with <c>/socket.io/</c>.
+    /// The client's BestHTTP <c>SocketManager</c> parses this string directly; a leading
+    /// <c>http://</c>/<c>https://</c> or a missing trailing slash will make the client
+    /// fail to connect. Host may be an IP, hostname, or FQDN.
+    /// <para>
+    /// Deployment-time value — no hardcoded fallback. Must be provided via the
+    /// <c>"BattleNode:NodeServerUrl"</c> key in <c>appsettings.json</c> (or an
+    /// equivalently-named env var); <see cref="Hosting.BattleNodeExtensions.AddBattleNode"/>
+    /// validates presence at startup and throws if empty.
+    /// </para>
+    /// </summary>
+    public string NodeServerUrl { get; set; } = "";
 
     /// <summary>
     /// How long the first arriver's WS waits for a partner before disconnecting.
diff --git a/SVSim.BattleNode/Hosting/BattleNodeExtensions.cs b/SVSim.BattleNode/Hosting/BattleNodeExtensions.cs
index 8c07fb8f..f2aa5125 100644
--- a/SVSim.BattleNode/Hosting/BattleNodeExtensions.cs
+++ b/SVSim.BattleNode/Hosting/BattleNodeExtensions.cs
@@ -18,15 +18,26 @@ public static class BattleNodeExtensions
     /// instance the WebSocket handler constructs on connect.
     /// </summary>
     /// <param name="configure">
-    /// Optional callback to override <see cref="BattleNodeOptions"/> defaults. The default
-    /// <c>NodeServerUrl</c> assumes the EmulatedEntrypoint host on
-    /// <c>http://localhost:5148</c> and shares the port for the Socket.IO endpoint. Override
-    /// when the node runs on a different port/host or behind a reverse proxy.
+    /// Callback to populate <see cref="BattleNodeOptions"/>. Must set
+    /// <see cref="BattleNodeOptions.NodeServerUrl"/> — there is no hardcoded fallback; the
+    /// value is a deployment concern (localhost during dev, a real host[:port]/socket.io/
+    /// when the node runs behind a reverse proxy or on a separate box). Startup throws
+    /// <see cref="InvalidOperationException"/> if it's still empty after the callback runs.
     /// </param>
+    /// <exception cref="InvalidOperationException">
+    /// <see cref="BattleNodeOptions.NodeServerUrl"/> is null, empty, or whitespace after
+    /// <paramref name="configure"/> runs.
+    /// </exception>
     public static IServiceCollection AddBattleNode(this IServiceCollection services, Action<BattleNodeOptions>? configure = null)
     {
         var options = new BattleNodeOptions();
         configure?.Invoke(options);
+        if (string.IsNullOrWhiteSpace(options.NodeServerUrl))
+        {
+            throw new InvalidOperationException(
+                "BattleNode:NodeServerUrl is not configured. Set it in appsettings.json under " +
+                "the \"BattleNode\" section (format: \"host[:port]/socket.io/\", no scheme prefix).");
+        }
         services.AddSingleton(options);
         services.AddSingleton<IBattleSessionStore, InMemoryBattleSessionStore>();
         services.AddSingleton<IMatchingBridge, MatchingBridge>();
diff --git a/SVSim.EmulatedEntrypoint/Program.cs b/SVSim.EmulatedEntrypoint/Program.cs
index 2acb5338..6c5c9164 100644
--- a/SVSim.EmulatedEntrypoint/Program.cs
+++ b/SVSim.EmulatedEntrypoint/Program.cs
@@ -165,11 +165,10 @@ public class Program
 
         builder.Services.AddBattleNode(opt =>
         {
-            // Matches the prod do_matching wire format: host:port/socket.io/, no scheme prefix.
-            // BestHTTP's SocketManager parses this as the Socket.IO v2 endpoint URL.
-            opt.NodeServerUrl = "localhost:5148/socket.io/";
-            // Any field in BattleNodeOptions can be overridden via the "BattleNode" section
-            // in appsettings*.json — see appsettings.Development.json for DiagnosticLogging.
+            // Every field on BattleNodeOptions is populated from the "BattleNode" section in
+            // appsettings*.json. NodeServerUrl has no hardcoded fallback — AddBattleNode
+            // throws at startup if it's missing/blank. See BattleNodeOptions.NodeServerUrl
+            // for the required wire format.
             builder.Configuration.GetSection("BattleNode").Bind(opt);
         });
         // In-process FCFS pair-up for TK2 PvP /do_matching, plus rank-battle's AI-fallback
diff --git a/SVSim.EmulatedEntrypoint/appsettings.json b/SVSim.EmulatedEntrypoint/appsettings.json
index dee87515..d0efef73 100644
--- a/SVSim.EmulatedEntrypoint/appsettings.json
+++ b/SVSim.EmulatedEntrypoint/appsettings.json
@@ -27,5 +27,13 @@
   "Deck": {
     "MaxDeckSlots": 36
   },
+  "BattleNode": {
+    // Socket.IO v2 endpoint URL echoed to the client on /*/do_matching success.
+    // Wire format: "host[:port]/socket.io/" — no scheme prefix, trailing slash REQUIRED.
+    // Host may be an IP, hostname, or FQDN. BestHTTP's SocketManager parses this string
+    // directly; a leading http:// or https:// will make the client fail to connect.
+    // Startup throws if this value is missing or blank; there is no hardcoded fallback.
+    "NodeServerUrl": "localhost:5148/socket.io/"
+  },
   "AllowedHosts": "*"
 }