diff --git a/docs/requirements/Component-ManagementService.md b/docs/requirements/Component-ManagementService.md
index 1dbcef5c..a9a04ff0 100644
--- a/docs/requirements/Component-ManagementService.md
+++ b/docs/requirements/Component-ManagementService.md
@@ -131,7 +131,7 @@ The whole folder surface is reachable from the CLI as `template folder list|crea
 ### Sites
 
 - **ListSites** / **GetSite**: Query site definitions.
-- **CreateSite** / **UpdateSite** / **DeleteSite**: Manage site definitions.
+- **CreateSite** / **UpdateSite** / **DeleteSite**: Manage site definitions. Create/Update validate `GrpcNodeAAddress` / `GrpcNodeBAddress` at the write boundary with `GrpcEndpointRules.TryValidate` (both optional; a non-empty value must be an absolute `http://` or `https://` URL with a host, e.g. `http://host:8083`) and reject a malformed value with a readable `COMMAND_FAILED` error naming the field — a scheme-less address used to be persisted and then throw inside central's channel build on the next site-address refresh (review 2026-10-21 03/R-1).
 - **ListAreas** / **CreateArea** / **UpdateArea** / **DeleteArea**: Manage area hierarchies per site.
 - **MoveArea** (`AreaId`, `NewParentAreaId?`): Re-parent an area within its own site; a null `NewParentAreaId` moves it to the site root. Delegates every rule to `AreaService.MoveAreaAsync` — rejects self-parent, descendant-parent (cycle), cross-site parent, and sibling name collision at the target level; the service writes the `"Move"` audit row. Same any-of `[Designer, Deployer]` gate as the other area mutations. CLI: `site area move`.
 
diff --git a/src/ZB.MOM.WW.ScadaBridge.ManagementService/ManagementActor.cs b/src/ZB.MOM.WW.ScadaBridge.ManagementService/ManagementActor.cs
index 9e9002f7..0cde809d 100644
--- a/src/ZB.MOM.WW.ScadaBridge.ManagementService/ManagementActor.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.ManagementService/ManagementActor.cs
@@ -29,6 +29,7 @@ using ZB.MOM.WW.ScadaBridge.Commons.Types.Deployment;
 using ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;
 using ZB.MOM.WW.ScadaBridge.Commons.Types.InboundApi;
 using ZB.MOM.WW.ScadaBridge.Commons.Types.Transport;
+using ZB.MOM.WW.ScadaBridge.Commons.Validation;
 using ZB.MOM.WW.ScadaBridge.DeploymentManager;
 using ZB.MOM.WW.ScadaBridge.HealthMonitoring;
 using ZB.MOM.WW.ScadaBridge.Communication;
@@ -1885,8 +1886,23 @@ public class ManagementActor : ReceiveActor
         return site;
     }
 
+    /// <summary>
+    /// Rejects a malformed site gRPC address at the write boundary (review 2026-10-21
+    /// 03/R-1). Both addresses are optional, but a non-empty value must be an absolute
+    /// http(s) URL — anything else makes the central channel build throw inside
+    /// <c>SitePairChannelProvider.UpdateSite</c> on the next address refresh.
+    /// </summary>
+    private static void ValidateSiteGrpcAddresses(string? grpcNodeAAddress, string? grpcNodeBAddress)
+    {
+        if (!GrpcEndpointRules.TryValidate(grpcNodeAAddress, allowEmpty: true, out var errorA))
+            throw new ManagementCommandException($"GrpcNodeAAddress: {errorA}");
+        if (!GrpcEndpointRules.TryValidate(grpcNodeBAddress, allowEmpty: true, out var errorB))
+            throw new ManagementCommandException($"GrpcNodeBAddress: {errorB}");
+    }
+
     private static async Task<object?> HandleCreateSite(IServiceProvider sp, CreateSiteCommand cmd, string user)
     {
+        ValidateSiteGrpcAddresses(cmd.GrpcNodeAAddress, cmd.GrpcNodeBAddress);
         var repo = sp.GetRequiredService<ISiteRepository>();
         var site = new Site(cmd.Name, cmd.SiteIdentifier)
         {
@@ -1906,6 +1922,7 @@ public class ManagementActor : ReceiveActor
 
     private static async Task<object?> HandleUpdateSite(IServiceProvider sp, UpdateSiteCommand cmd, string user)
     {
+        ValidateSiteGrpcAddresses(cmd.GrpcNodeAAddress, cmd.GrpcNodeBAddress);
         var repo = sp.GetRequiredService<ISiteRepository>();
         var site = await repo.GetSiteByIdAsync(cmd.SiteId)
             ?? throw new ManagementCommandException($"Site with ID {cmd.SiteId} not found.");
diff --git a/tests/ZB.MOM.WW.ScadaBridge.ManagementService.Tests/SiteGrpcEndpointValidationTests.cs b/tests/ZB.MOM.WW.ScadaBridge.ManagementService.Tests/SiteGrpcEndpointValidationTests.cs
new file mode 100644
index 00000000..3b9968ac
--- /dev/null
+++ b/tests/ZB.MOM.WW.ScadaBridge.ManagementService.Tests/SiteGrpcEndpointValidationTests.cs
@@ -0,0 +1,80 @@
+using Akka.Actor;
+using Akka.TestKit.Xunit2;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging.Abstractions;
+using NSubstitute;
+using ZB.MOM.WW.ScadaBridge.Commons.Entities.Sites;
+using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Repositories;
+using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Services;
+using ZB.MOM.WW.ScadaBridge.Commons.Messages.Management;
+
+namespace ZB.MOM.WW.ScadaBridge.ManagementService.Tests;
+
+/// <summary>
+/// Review 2026-10-21 03/R-1: a malformed site gRPC address used to be persisted
+/// unvalidated and then throw inside <c>SitePairChannelProvider.UpdateSite</c>.
+/// Create/Update must reject it at the write boundary with a readable error.
+/// </summary>
+public class SiteGrpcEndpointValidationTests : TestKit
+{
+    private readonly ISiteRepository _siteRepo = Substitute.For<ISiteRepository>();
+    private readonly ServiceCollection _services;
+
+    /// <summary>Initializes the harness.</summary>
+    public SiteGrpcEndpointValidationTests()
+    {
+        _services = new ServiceCollection().AddTestConfigurationTransaction();
+        _services.AddScoped(_ => _siteRepo);
+        _services.AddScoped(_ => Substitute.For<IAuditService>());
+        _siteRepo.GetSiteByIdAsync(7, Arg.Any<CancellationToken>())
+            .Returns(new Site("S", "S1") { Id = 7 });
+    }
+
+    private IActorRef CreateActor() =>
+        Sys.ActorOf(Props.Create(() => new ManagementActor(
+            _services.BuildServiceProvider(), NullLogger<ManagementActor>.Instance)));
+
+    private static ManagementEnvelope Admin(object command) =>
+        new(new AuthenticatedUser("admin", "Admin", new[] { "Administrator" }, Array.Empty<string>()),
+            command, Guid.NewGuid().ToString("N"));
+
+    /// <summary>Create with a scheme-less node-A address is rejected and nothing is saved.</summary>
+    [Theory]
+    [InlineData("scadabridge-site-a-node-a")]
+    [InlineData("site-a-node-a:8083")]
+    [InlineData("ftp://host:8083")]
+    public void CreateSite_MalformedGrpcAddress_ReturnsReadableError(string bad)
+    {
+        var actor = CreateActor();
+        actor.Tell(Admin(new CreateSiteCommand("S", "S1", null, GrpcNodeAAddress: bad)));
+
+        var error = ExpectMsg<ManagementError>(TimeSpan.FromSeconds(5));
+        Assert.Contains("GrpcNodeAAddress", error.Error);
+        Assert.Contains("http://", error.Error);
+        _siteRepo.DidNotReceive().AddSiteAsync(Arg.Any<Site>(), Arg.Any<CancellationToken>());
+    }
+
+    /// <summary>Update with a malformed node-B address is rejected and nothing is saved.</summary>
+    [Fact]
+    public void UpdateSite_MalformedGrpcNodeB_ReturnsReadableError()
+    {
+        var actor = CreateActor();
+        actor.Tell(Admin(new UpdateSiteCommand(7, "S", null,
+            GrpcNodeAAddress: "http://a:8083", GrpcNodeBAddress: "b:8083")));
+
+        var error = ExpectMsg<ManagementError>(TimeSpan.FromSeconds(5));
+        Assert.Contains("GrpcNodeBAddress", error.Error);
+        _siteRepo.DidNotReceive().UpdateSiteAsync(Arg.Any<Site>(), Arg.Any<CancellationToken>());
+    }
+
+    /// <summary>Both gRPC addresses are optional; valid http(s) URLs (and blanks) are accepted.</summary>
+    [Fact]
+    public void CreateSite_ValidOrEmptyGrpcAddresses_Succeeds()
+    {
+        var actor = CreateActor();
+        actor.Tell(Admin(new CreateSiteCommand("S", "S1", null,
+            GrpcNodeAAddress: "http://site-a-node-a:8083", GrpcNodeBAddress: null)));
+
+        ExpectMsg<ManagementSuccess>(TimeSpan.FromSeconds(5));
+    }
+}