diff --git a/docs/EventSourceAndCounters.md b/docs/EventSourceAndCounters.md
index 36afedf91a23..fb2416531eec 100644
--- a/docs/EventSourceAndCounters.md
+++ b/docs/EventSourceAndCounters.md
@@ -169,7 +169,34 @@ namespace Microsoft.AspNetCore.Authentication.Internal
 
 ## Automated Testing of EventSources
 
-EventSources can be tested using the `EventSourceTestBase` base class in `Microsoft.AspNetCore.InternalTesting`. An example test is below:
+### Validating Event ID Consistency
+
+All `EventSource` subclasses should have a test that validates the `[Event(N)]` attribute IDs match the `WriteEvent(N, ...)` call arguments. This catches drift caused by bad merge resolution or missed updates that would otherwise surface only as runtime errors.
+
+Use the `EventSourceValidator` utility in `Microsoft.AspNetCore.InternalTesting.Tracing`:
+
+```csharp
+using Microsoft.AspNetCore.InternalTesting.Tracing;
+
+public class MyEventSourceTests
+{
+    [Fact]
+    public void EventIdsAreConsistent()
+    {
+        EventSourceValidator.ValidateEventSourceIds<MyEventSource>();
+    }
+}
+```
+
+The validator:
+* Uses `EventSource.GenerateManifest` with `EventManifestOptions.Strict` to perform IL-level validation that each `WriteEvent(id, ...)` call argument matches the `[Event(id)]` attribute — the same validation the .NET runtime uses internally
+* Checks for duplicate event IDs across methods
+
+> **Important:** Every new `EventSource` class should include this one-line validation test.
+
+### Functional Testing with EventSourceTestBase
+
+EventSources can also be functionally tested using the `EventSourceTestBase` base class in `Microsoft.AspNetCore.InternalTesting`. An example test is below:
 
 ```csharp
 // The base class MUST be used for EventSource testing because EventSources are global and parallel tests can cause issues.
diff --git a/src/Hosting/Hosting/test/Internal/HostingEventSourceTests.cs b/src/Hosting/Hosting/test/Internal/HostingEventSourceTests.cs
index 2fd4b40376da..d3edd323b854 100644
--- a/src/Hosting/Hosting/test/Internal/HostingEventSourceTests.cs
+++ b/src/Hosting/Hosting/test/Internal/HostingEventSourceTests.cs
@@ -6,12 +6,19 @@
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Internal;
 using Microsoft.AspNetCore.InternalTesting;
+using Microsoft.AspNetCore.InternalTesting.Tracing;
 using Microsoft.Extensions.Logging;
 
 namespace Microsoft.AspNetCore.Hosting;
 
 public class HostingEventSourceTests : LoggedTest
 {
+    [Fact]
+    public void EventIdsAreConsistent()
+    {
+        EventSourceValidator.ValidateEventSourceIds(typeof(HostingEventSource));
+    }
+
     [Fact]
     public void MatchesNameAndGuid()
     {
diff --git a/src/Servers/Kestrel/Core/test/KestrelEventSourceTests.cs b/src/Servers/Kestrel/Core/test/KestrelEventSourceTests.cs
index 4a81affd241f..11a69c0efabc 100644
--- a/src/Servers/Kestrel/Core/test/KestrelEventSourceTests.cs
+++ b/src/Servers/Kestrel/Core/test/KestrelEventSourceTests.cs
@@ -5,6 +5,7 @@
 using System.Diagnostics.Tracing;
 using System.Globalization;
 using System.Reflection;
+using Microsoft.AspNetCore.InternalTesting.Tracing;
 using Xunit;
 
 namespace Microsoft.AspNetCore.Server.Kestrel.Core.Tests;
@@ -26,4 +27,16 @@ public void ExistsWithCorrectId()
         Assert.Equal(Guid.Parse("bdeb4676-a36e-5442-db99-4764e2326c7d", CultureInfo.InvariantCulture), EventSource.GetGuid(esType));
         Assert.NotEmpty(EventSource.GenerateManifest(esType, "assemblyPathToIncludeInManifest"));
     }
+
+    [Fact]
+    public void EventIdsAreConsistent()
+    {
+        var esType = typeof(KestrelServer).Assembly.GetType(
+            "Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure.KestrelEventSource",
+            throwOnError: true,
+            ignoreCase: false
+        );
+
+        EventSourceValidator.ValidateEventSourceIds(esType);
+    }
 }
diff --git a/src/Shared/test/Shared.Tests/CertificateManagerEventSourceTests.cs b/src/Shared/test/Shared.Tests/CertificateManagerEventSourceTests.cs
new file mode 100644
index 000000000000..b23eab74809c
--- /dev/null
+++ b/src/Shared/test/Shared.Tests/CertificateManagerEventSourceTests.cs
@@ -0,0 +1,16 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.AspNetCore.Certificates.Generation;
+using Microsoft.AspNetCore.InternalTesting.Tracing;
+
+namespace Microsoft.AspNetCore.Internal.Tests;
+
+public class CertificateManagerEventSourceTests
+{
+    [Fact]
+    public void EventIdsAreConsistent()
+    {
+        EventSourceValidator.ValidateEventSourceIds<CertificateManager.CertificateManagerEventSource>();
+    }
+}
diff --git a/src/SignalR/common/Http.Connections/test/Internal/HttpConnectionsEventSourceTests.cs b/src/SignalR/common/Http.Connections/test/Internal/HttpConnectionsEventSourceTests.cs
index 40b4ce1b4c8b..567ac8c75809 100644
--- a/src/SignalR/common/Http.Connections/test/Internal/HttpConnectionsEventSourceTests.cs
+++ b/src/SignalR/common/Http.Connections/test/Internal/HttpConnectionsEventSourceTests.cs
@@ -6,6 +6,7 @@
 using System.Diagnostics.Tracing;
 using System.Globalization;
 using Microsoft.AspNetCore.Internal;
+using Microsoft.AspNetCore.InternalTesting.Tracing;
 using Microsoft.Extensions.Internal;
 using Xunit;
 
@@ -13,6 +14,12 @@ namespace Microsoft.AspNetCore.Http.Connections.Internal;
 
 public class HttpConnectionsEventSourceTests
 {
+    [Fact]
+    public void EventIdsAreConsistent()
+    {
+        EventSourceValidator.ValidateEventSourceIds(typeof(HttpConnectionsEventSource));
+    }
+
     [Fact]
     public void MatchesNameAndGuid()
     {
diff --git a/src/Testing/src/Tracing/EventSourceValidator.cs b/src/Testing/src/Tracing/EventSourceValidator.cs
new file mode 100644
index 000000000000..459f5edeb696
--- /dev/null
+++ b/src/Testing/src/Tracing/EventSourceValidator.cs
@@ -0,0 +1,106 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.Tracing;
+using System.Reflection;
+using Xunit;
+
+namespace Microsoft.AspNetCore.InternalTesting.Tracing;
+
+/// <summary>
+/// Validates that <see cref="EventSource"/>-derived classes have consistent
+/// <see cref="EventAttribute.EventId"/> values and <c>WriteEvent</c> call arguments.
+/// This catches drift caused by bad merge resolution or missed updates that would
+/// otherwise surface only as runtime errors.
+/// </summary>
+public static class EventSourceValidator
+{
+    /// <summary>
+    /// Validates all <c>[Event]</c>-attributed methods on <typeparamref name="T"/>.
+    /// </summary>
+    /// <typeparam name="T">A type that derives from <see cref="EventSource"/>.</typeparam>
+    public static void ValidateEventSourceIds<T>() where T : EventSource
+        => ValidateEventSourceIds(typeof(T));
+
+    /// <summary>
+    /// Validates all <c>[Event]</c>-attributed methods on the given <see cref="EventSource"/>-derived type.
+    /// <para>
+    /// Uses <see cref="EventSource.GenerateManifest(Type, string, EventManifestOptions)"/> with
+    /// <see cref="EventManifestOptions.Strict"/> to perform IL-level validation that the integer
+    /// argument passed to each <c>WriteEvent</c> call matches the <c>[Event(id)]</c> attribute
+    /// on the calling method. This is the same validation the .NET runtime itself uses.
+    /// </para>
+    /// <para>
+    /// Additionally checks for duplicate <see cref="EventAttribute.EventId"/> values across methods.
+    /// </para>
+    /// </summary>
+    /// <param name="eventSourceType">A type that derives from <see cref="EventSource"/>.</param>
+    public static void ValidateEventSourceIds(Type eventSourceType)
+    {
+        if (eventSourceType is null)
+        {
+            throw new ArgumentNullException(nameof(eventSourceType));
+        }
+
+        Assert.True(
+            typeof(EventSource).IsAssignableFrom(eventSourceType),
+            $"Type '{eventSourceType.FullName}' does not derive from EventSource.");
+
+        var errors = new List<string>();
+
+        // Check for duplicate Event IDs across methods.
+        var seenIds = new Dictionary<int, string>();
+        var methods = eventSourceType.GetMethods(
+            BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.DeclaredOnly);
+
+        foreach (var method in methods)
+        {
+            var eventAttr = method.GetCustomAttribute<EventAttribute>();
+            if (eventAttr is null)
+            {
+                continue;
+            }
+
+            if (seenIds.TryGetValue(eventAttr.EventId, out var existingMethod))
+            {
+                errors.Add(
+                    $"Duplicate EventId {eventAttr.EventId}: methods '{existingMethod}' and '{method.Name}' share the same ID.");
+            }
+            else
+            {
+                seenIds[eventAttr.EventId] = method.Name;
+            }
+        }
+
+        // Use GenerateManifest with Strict mode to validate that each method's
+        // WriteEvent(id, ...) call uses an ID that matches its [Event(id)] attribute.
+        // Internally this uses GetHelperCallFirstArg to IL-inspect the method body
+        // and extract the integer constant passed to WriteEvent — the same validation
+        // the .NET runtime performs when constructing an EventSource.
+        try
+        {
+            var manifest = EventSource.GenerateManifest(
+                eventSourceType,
+                assemblyPathToIncludeInManifest: "assemblyPathForValidation",
+                flags: EventManifestOptions.Strict);
+
+            if (manifest is null)
+            {
+                errors.Add("GenerateManifest returned null, indicating the type is not a valid EventSource.");
+            }
+        }
+        catch (ArgumentException ex)
+        {
+            errors.Add(ex.Message);
+        }
+
+        if (errors.Count > 0)
+        {
+            Assert.Fail(
+                $"EventSource '{eventSourceType.FullName}' has event ID validation error(s):" +
+                Environment.NewLine + string.Join(Environment.NewLine, errors));
+        }
+    }
+}
diff --git a/src/Testing/test/EventSourceValidatorTests.cs b/src/Testing/test/EventSourceValidatorTests.cs
new file mode 100644
index 000000000000..b6a1d3130141
--- /dev/null
+++ b/src/Testing/test/EventSourceValidatorTests.cs
@@ -0,0 +1,119 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Diagnostics.Tracing;
+using Microsoft.AspNetCore.InternalTesting.Tracing;
+using Xunit;
+
+namespace Microsoft.AspNetCore.InternalTesting;
+
+public class EventSourceValidatorTests
+{
+    [Fact]
+    public void ValidateEventSourceIds_PassesForCorrectEventSource()
+    {
+        EventSourceValidator.ValidateEventSourceIds<CorrectEventSource>();
+    }
+
+    [Fact]
+    public void ValidateEventSourceIds_FailsForMismatchedWriteEventId()
+    {
+        // GenerateManifest(Strict) detects the mismatch via IL inspection
+        // and our validator surfaces it through Assert.Fail.
+        // The exact runtime error message varies by .NET version, so we
+        // only verify the validator rejects the bad source.
+        Assert.ThrowsAny<Exception>(
+            () => EventSourceValidator.ValidateEventSourceIds<MismatchedIdEventSource>());
+    }
+
+    [Fact]
+    public void ValidateEventSourceIds_FailsForDuplicateEventIds()
+    {
+        // The duplicate ID message is produced by our validator code.
+        var ex = Assert.ThrowsAny<Exception>(
+            () => EventSourceValidator.ValidateEventSourceIds<DuplicateIdEventSource>());
+
+        Assert.Contains("Duplicate EventId 1", ex.Message);
+        Assert.Contains("EventAlpha", ex.Message);
+        Assert.Contains("EventBeta", ex.Message);
+    }
+
+    [Fact]
+    public void ValidateEventSourceIds_FailsForNonEventSourceType()
+    {
+        // The guard clause message is produced by our validator code.
+        var ex = Assert.ThrowsAny<Exception>(
+            () => EventSourceValidator.ValidateEventSourceIds(typeof(string)));
+
+        Assert.Contains("does not derive from EventSource", ex.Message);
+    }
+
+    [Fact]
+    public void ValidateEventSourceIds_PassesForEventSourceWithNoEvents()
+    {
+        EventSourceValidator.ValidateEventSourceIds<EmptyEventSource>();
+    }
+
+    [Fact]
+    public void ValidateEventSourceIds_PassesForEventSourceWithMultipleParameterTypes()
+    {
+        EventSourceValidator.ValidateEventSourceIds<MultiParamEventSource>();
+    }
+
+    // -- Test-only EventSource implementations --
+
+    [EventSource(Name = "Test-Correct")]
+    private sealed class CorrectEventSource : EventSource
+    {
+        [Event(1, Level = EventLevel.Informational)]
+        public void EventOne(string message) => WriteEvent(1, message);
+
+        [Event(2, Level = EventLevel.Verbose)]
+        public void EventTwo(int count) => WriteEvent(2, count);
+
+        [Event(3, Level = EventLevel.Warning)]
+        public void EventThree() => WriteEvent(3);
+    }
+
+    [EventSource(Name = "Test-MismatchedId")]
+    private sealed class MismatchedIdEventSource : EventSource
+    {
+        [Event(1, Level = EventLevel.Informational)]
+        public void EventOne(int value) => WriteEvent(99, value);
+    }
+
+    [EventSource(Name = "Test-DuplicateId")]
+    private sealed class DuplicateIdEventSource : EventSource
+    {
+        [Event(1, Level = EventLevel.Informational)]
+        public void EventAlpha(string message) => WriteEvent(1, message);
+
+        [Event(1, Level = EventLevel.Informational)]
+        public void EventBeta(int count) => WriteEvent(1, count);
+    }
+
+    [EventSource(Name = "Test-Empty")]
+    private sealed class EmptyEventSource : EventSource
+    {
+    }
+
+    [EventSource(Name = "Test-MultiParam")]
+    private sealed class MultiParamEventSource : EventSource
+    {
+        [Event(1, Level = EventLevel.Informational)]
+        public void EventWithString(string value) => WriteEvent(1, value);
+
+        [Event(2, Level = EventLevel.Informational)]
+        public void EventWithInt(int value) => WriteEvent(2, value);
+
+        [Event(3, Level = EventLevel.Informational)]
+        public void EventWithLong(long value) => WriteEvent(3, value);
+
+        [Event(4, Level = EventLevel.Informational)]
+        public void EventWithMultiple(string name, int count) => WriteEvent(4, name, count);
+
+        [Event(5, Level = EventLevel.Informational)]
+        public void EventWithNoArgs() => WriteEvent(5);
+    }
+}