Fix ClientErrorMapping 500 title to match RFC 9110 by kubaflo · Pull Request #65590 · dotnet/aspnetcore

kubaflo · 2026-03-01T18:08:19Z

🤖 AI Summary

🔍 Automated Fix Report

🔍 Pre-Flight — Context & Validation

Issue: #16880 - Inconsistency between ApiBehaviorOptions.ClientErrorMapping and ReasonPhrases using 500
Area: area-mvc (src/Shared/ProblemDetails/, src/Mvc/Mvc.Core/)
PR: None — will create

Key Findings

ProblemDetailsDefaults.cs line 136: 500 title is "An error occurred while processing your request."
ReasonPhrases.GetReasonPhrase(500) returns "Internal Server Error" (RFC 9110)
All other status codes in ProblemDetailsDefaults use RFC standard reason phrases
Team member @pranavkm confirmed: "we should update MVC to do the same for 500"
@Tratcher confirmed: "ReasonPhrases are RFC defined values and should not be modified"

Fix Approach

Change the 500 title in ProblemDetailsDefaults.cs from "An error occurred..." to "Internal Server Error" to match RFC 9110 and ReasonPhrases.

Test Command

dotnet test src/Mvc/Mvc.Core/test/Microsoft.AspNetCore.Mvc.Core.Test.csproj --filter "ProblemDetailsFactoryTest"

🧪 Test — Bug Reproduction

Test Result: ✅ TESTS UPDATED

Existing tests already verify the 500 title value. Updated 9 test assertions across 7 files to expect "Internal Server Error" instead of "An error occurred while processing your request."

🚦 Gate — Test Verification & Regression

Gate Result: ✅ PASSED

All affected tests pass with the updated title string.

🔧 Fix — Analysis & Comparison (✅ 5 passed)

Fix Exploration Summary

Total Attempts: 5
Passing Candidates: 5
Selected Fix: Change "An error occurred while processing your request." to "Internal Server Error"

Attempt Results

#	Model	Approach	Result	Key Insight
0	claude-opus-4.6-fast	Change string constant to RFC 9110 value	✅ Pass	Only correct fix
1	claude-sonnet-4.6	Same — string constant fix	✅ Pass	Converges to same fix
2	gpt-5.2	Same — string constant fix	✅ Pass	Converges to same fix
3	gpt-5.3-codex	Same — string constant fix	✅ Pass	Converges to same fix
4	gemini-3-pro-preview	Same — string constant fix	✅ Pass	Converges to same fix

Cross-Pollination

All models agree: there is exactly one correct value — "Internal Server Error" from RFC 9110.

Exhausted: Yes

Recommendation

This is a trivial fix with only one correct answer. All models converge to the same solution.

✅ Attempt 0: PASS

Attempt 0 — Baseline (claude-opus-4.6-fast)

Approach: Change ProblemDetailsDefaults.cs line 136 from "An error occurred while processing your request." to "Internal Server Error"

Simple one-line fix + 9 test assertion updates.

📄 Diff

diff --git a/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs b/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs
index 2afabbec3f..b36499ee52 100644
--- a/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs
+++ b/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs
@@ -560,7 +560,7 @@ public partial class DefaultProblemDetailsWriterTest
         Assert.NotNull(problemDetails);
         Assert.Equal(StatusCodes.Status500InternalServerError, problemDetails.Status);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", problemDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", problemDetails.Title);
+        Assert.Equal("Internal Server Error", problemDetails.Title);
         Assert.Equal(expectedTraceId, problemDetails.Extensions["traceId"].ToString());
     }
 
diff --git a/src/Http/Http.Results/test/JsonResultTests.cs b/src/Http/Http.Results/test/JsonResultTests.cs
index 6e2b05dbcc..3af14f6f24 100644
--- a/src/Http/Http.Results/test/JsonResultTests.cs
+++ b/src/Http/Http.Results/test/JsonResultTests.cs
@@ -139,7 +139,7 @@ public class JsonResultTests
         stream.Position = 0;
         var responseDetails = JsonSerializer.Deserialize<ProblemDetails>(stream, JsonSerializerOptions.Web);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", responseDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", responseDetails.Title);
+        Assert.Equal("Internal Server Error", responseDetails.Title);
         Assert.Equal(StatusCodes.Status500InternalServerError, responseDetails.Status);
     }
 
diff --git a/src/Http/Http.Results/test/ProblemResultTests.cs b/src/Http/Http.Results/test/ProblemResultTests.cs
index c01c42a5d2..8e41555548 100644
--- a/src/Http/Http.Results/test/ProblemResultTests.cs
+++ b/src/Http/Http.Results/test/ProblemResultTests.cs
@@ -37,7 +37,7 @@ public class ProblemResultTests
         stream.Position = 0;
         var responseDetails = JsonSerializer.Deserialize<ProblemDetails>(stream, JsonSerializerOptions.Web);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", responseDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", responseDetails.Title);
+        Assert.Equal("Internal Server Error", responseDetails.Title);
         Assert.Equal(StatusCodes.Status500InternalServerError, responseDetails.Status);
     }
 
@@ -69,7 +69,7 @@ public class ProblemResultTests
         stream.Position = 0;
         var responseDetails = JsonSerializer.Deserialize<ProblemDetails>(stream, JsonSerializerOptions.Web);
         Assert.Null(responseDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", responseDetails.Title);
+        Assert.Equal("Internal Server Error", responseDetails.Title);
         Assert.Equal(StatusCodes.Status500InternalServerError, responseDetails.Status);
     }
 
diff --git a/src/Http/Http.Results/test/ResultsTests.cs b/src/Http/Http.Results/test/ResultsTests.cs
index ce87ee10e9..e21d097b48 100644
--- a/src/Http/Http.Results/test/ResultsTests.cs
+++ b/src/Http/Http.Results/test/ResultsTests.cs
@@ -1349,7 +1349,7 @@ public partial class ResultsTests
         Assert.Null(result.ProblemDetails.Instance);
         Assert.Equal("application/problem+json", result.ContentType);
         Assert.Equal(StatusCodes.Status500InternalServerError, result.StatusCode);
-        Assert.Equal("An error occurred while processing your request.", result.ProblemDetails.Title);
+        Assert.Equal("Internal Server Error", result.ProblemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", result.ProblemDetails.Type);
         Assert.Empty(result.ProblemDetails.Extensions);
     }
diff --git a/src/Http/Http.Results/test/TypedResultsTests.cs b/src/Http/Http.Results/test/TypedResultsTests.cs
index acee20c4d1..cef21cda67 100644
--- a/src/Http/Http.Results/test/TypedResultsTests.cs
+++ b/src/Http/Http.Results/test/TypedResultsTests.cs
@@ -1141,7 +1141,7 @@ public partial class TypedResultsTests
         Assert.Null(result.ProblemDetails.Instance);
         Assert.Equal("application/problem+json", result.ContentType);
         Assert.Equal(StatusCodes.Status500InternalServerError, result.StatusCode);
-        Assert.Equal("An error occurred while processing your request.", result.ProblemDetails.Title);
+        Assert.Equal("Internal Server Error", result.ProblemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", result.ProblemDetails.Type);
         Assert.Empty(result.ProblemDetails.Extensions);
     }
diff --git a/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs b/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs
index fd502060bf..c9a97ed0f3 100644
--- a/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs
+++ b/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs
@@ -2475,7 +2475,7 @@ public class ControllerBaseTest
         var problemDetails = Assert.IsType<ProblemDetails>(badRequestResult.Value);
         Assert.Equal(500, actionResult.StatusCode);
         Assert.Equal(500, problemDetails.Status);
-        Assert.Equal("An error occurred while processing your request.", problemDetails.Title);
+        Assert.Equal("Internal Server Error", problemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", problemDetails.Type);
         Assert.Equal("some-trace", problemDetails.Extensions["traceId"]);
     }
@@ -2568,7 +2568,7 @@ public class ControllerBaseTest
                     },
                     [500] = new ClientErrorData
                     {
-                        Title = "An error occurred while processing your request.",
+                        Title = "Internal Server Error",
                         Link = "https://tools.ietf.org/html/rfc9110#section-15.6.1"
                     }
                 }
diff --git a/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs b/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs
index 2695b167ff..d8aa6ac0e8 100644
--- a/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs
+++ b/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs
@@ -20,7 +20,7 @@ public class ProblemDetailsFactoryTest
 
         // Assert
         Assert.Equal(500, problemDetails.Status);
-        Assert.Equal("An error occurred while processing your request.", problemDetails.Title);
+        Assert.Equal("Internal Server Error", problemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", problemDetails.Type);
         Assert.Null(problemDetails.Instance);
         Assert.Null(problemDetails.Detail);
diff --git a/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs b/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs
index 967c1aa486..b8d3a18fe2 100644
--- a/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs
+++ b/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs
@@ -133,7 +133,7 @@ internal static class ProblemDetailsDefaults
         [500] =
         (
             "https://tools.ietf.org/html/rfc9110#section-15.6.1",
-            "An error occurred while processing your request."
+            "Internal Server Error"
         ),
 
         [501] =

✅ Attempt 1: PASS

Attempt 1 — Model exploration

Approach: Same as attempt 0 — this is a string constant fix with only one correct value.
The 500 title must match RFC 9110: "Internal Server Error". There is no alternative approach.

📄 Diff

diff --git a/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs b/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs
index 2afabbec3f..b36499ee52 100644
--- a/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs
+++ b/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs
@@ -560,7 +560,7 @@ public partial class DefaultProblemDetailsWriterTest
         Assert.NotNull(problemDetails);
         Assert.Equal(StatusCodes.Status500InternalServerError, problemDetails.Status);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", problemDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", problemDetails.Title);
+        Assert.Equal("Internal Server Error", problemDetails.Title);
         Assert.Equal(expectedTraceId, problemDetails.Extensions["traceId"].ToString());
     }
 
diff --git a/src/Http/Http.Results/test/JsonResultTests.cs b/src/Http/Http.Results/test/JsonResultTests.cs
index 6e2b05dbcc..3af14f6f24 100644
--- a/src/Http/Http.Results/test/JsonResultTests.cs
+++ b/src/Http/Http.Results/test/JsonResultTests.cs
@@ -139,7 +139,7 @@ public class JsonResultTests
         stream.Position = 0;
         var responseDetails = JsonSerializer.Deserialize<ProblemDetails>(stream, JsonSerializerOptions.Web);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", responseDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", responseDetails.Title);
+        Assert.Equal("Internal Server Error", responseDetails.Title);
         Assert.Equal(StatusCodes.Status500InternalServerError, responseDetails.Status);
     }
 
diff --git a/src/Http/Http.Results/test/ProblemResultTests.cs b/src/Http/Http.Results/test/ProblemResultTests.cs
index c01c42a5d2..8e41555548 100644
--- a/src/Http/Http.Results/test/ProblemResultTests.cs
+++ b/src/Http/Http.Results/test/ProblemResultTests.cs
@@ -37,7 +37,7 @@ public class ProblemResultTests
         stream.Position = 0;
         var responseDetails = JsonSerializer.Deserialize<ProblemDetails>(stream, JsonSerializerOptions.Web);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", responseDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", responseDetails.Title);
+        Assert.Equal("Internal Server Error", responseDetails.Title);
         Assert.Equal(StatusCodes.Status500InternalServerError, responseDetails.Status);
     }
 
@@ -69,7 +69,7 @@ public class ProblemResultTests
         stream.Position = 0;
         var responseDetails = JsonSerializer.Deserialize<ProblemDetails>(stream, JsonSerializerOptions.Web);
         Assert.Null(responseDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", responseDetails.Title);
+        Assert.Equal("Internal Server Error", responseDetails.Title);
         Assert.Equal(StatusCodes.Status500InternalServerError, responseDetails.Status);
     }
 
diff --git a/src/Http/Http.Results/test/ResultsTests.cs b/src/Http/Http.Results/test/ResultsTests.cs
index ce87ee10e9..e21d097b48 100644
--- a/src/Http/Http.Results/test/ResultsTests.cs
+++ b/src/Http/Http.Results/test/ResultsTests.cs
@@ -1349,7 +1349,7 @@ public partial class ResultsTests
         Assert.Null(result.ProblemDetails.Instance);
         Assert.Equal("application/problem+json", result.ContentType);
         Assert.Equal(StatusCodes.Status500InternalServerError, result.StatusCode);
-        Assert.Equal("An error occurred while processing your request.", result.ProblemDetails.Title);
+        Assert.Equal("Internal Server Error", result.ProblemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", result.ProblemDetails.Type);
         Assert.Empty(result.ProblemDetails.Extensions);
     }
diff --git a/src/Http/Http.Results/test/TypedResultsTests.cs b/src/Http/Http.Results/test/TypedResultsTests.cs
index acee20c4d1..cef21cda67 100644
--- a/src/Http/Http.Results/test/TypedResultsTests.cs
+++ b/src/Http/Http.Results/test/TypedResultsTests.cs
@@ -1141,7 +1141,7 @@ public partial class TypedResultsTests
         Assert.Null(result.ProblemDetails.Instance);
         Assert.Equal("application/problem+json", result.ContentType);
         Assert.Equal(StatusCodes.Status500InternalServerError, result.StatusCode);
-        Assert.Equal("An error occurred while processing your request.", result.ProblemDetails.Title);
+        Assert.Equal("Internal Server Error", result.ProblemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", result.ProblemDetails.Type);
         Assert.Empty(result.ProblemDetails.Extensions);
     }
diff --git a/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs b/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs
index fd502060bf..c9a97ed0f3 100644
--- a/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs
+++ b/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs
@@ -2475,7 +2475,7 @@ public class ControllerBaseTest
         var problemDetails = Assert.IsType<ProblemDetails>(badRequestResult.Value);
         Assert.Equal(500, actionResult.StatusCode);
         Assert.Equal(500, problemDetails.Status);
-        Assert.Equal("An error occurred while processing your request.", problemDetails.Title);
+        Assert.Equal("Internal Server Error", problemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", problemDetails.Type);
         Assert.Equal("some-trace", problemDetails.Extensions["traceId"]);
     }
@@ -2568,7 +2568,7 @@ public class ControllerBaseTest
                     },
                     [500] = new ClientErrorData
                     {
-                        Title = "An error occurred while processing your request.",
+                        Title = "Internal Server Error",
                         Link = "https://tools.ietf.org/html/rfc9110#section-15.6.1"
                     }
                 }
diff --git a/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs b/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs
index 2695b167ff..d8aa6ac0e8 100644
--- a/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs
+++ b/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs
@@ -20,7 +20,7 @@ public class ProblemDetailsFactoryTest
 
         // Assert
         Assert.Equal(500, problemDetails.Status);
-        Assert.Equal("An error occurred while processing your request.", problemDetails.Title);
+        Assert.Equal("Internal Server Error", problemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", problemDetails.Type);
         Assert.Null(problemDetails.Instance);
         Assert.Null(problemDetails.Detail);
diff --git a/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs b/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs
index 967c1aa486..b8d3a18fe2 100644
--- a/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs
+++ b/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs
@@ -133,7 +133,7 @@ internal static class ProblemDetailsDefaults
         [500] =
         (
             "https://tools.ietf.org/html/rfc9110#section-15.6.1",
-            "An error occurred while processing your request."
+            "Internal Server Error"
         ),
 
         [501] =

✅ Attempt 2: PASS

Attempt 2 — Model exploration

Approach: Same as attempt 0 — this is a string constant fix with only one correct value.
The 500 title must match RFC 9110: "Internal Server Error". There is no alternative approach.

📄 Diff

diff --git a/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs b/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs
index 2afabbec3f..b36499ee52 100644
--- a/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs
+++ b/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs
@@ -560,7 +560,7 @@ public partial class DefaultProblemDetailsWriterTest
         Assert.NotNull(problemDetails);
         Assert.Equal(StatusCodes.Status500InternalServerError, problemDetails.Status);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", problemDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", problemDetails.Title);
+        Assert.Equal("Internal Server Error", problemDetails.Title);
         Assert.Equal(expectedTraceId, problemDetails.Extensions["traceId"].ToString());
     }
 
diff --git a/src/Http/Http.Results/test/JsonResultTests.cs b/src/Http/Http.Results/test/JsonResultTests.cs
index 6e2b05dbcc..3af14f6f24 100644
--- a/src/Http/Http.Results/test/JsonResultTests.cs
+++ b/src/Http/Http.Results/test/JsonResultTests.cs
@@ -139,7 +139,7 @@ public class JsonResultTests
         stream.Position = 0;
         var responseDetails = JsonSerializer.Deserialize<ProblemDetails>(stream, JsonSerializerOptions.Web);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", responseDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", responseDetails.Title);
+        Assert.Equal("Internal Server Error", responseDetails.Title);
         Assert.Equal(StatusCodes.Status500InternalServerError, responseDetails.Status);
     }
 
diff --git a/src/Http/Http.Results/test/ProblemResultTests.cs b/src/Http/Http.Results/test/ProblemResultTests.cs
index c01c42a5d2..8e41555548 100644
--- a/src/Http/Http.Results/test/ProblemResultTests.cs
+++ b/src/Http/Http.Results/test/ProblemResultTests.cs
@@ -37,7 +37,7 @@ public class ProblemResultTests
         stream.Position = 0;
         var responseDetails = JsonSerializer.Deserialize<ProblemDetails>(stream, JsonSerializerOptions.Web);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", responseDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", responseDetails.Title);
+        Assert.Equal("Internal Server Error", responseDetails.Title);
         Assert.Equal(StatusCodes.Status500InternalServerError, responseDetails.Status);
     }
 
@@ -69,7 +69,7 @@ public class ProblemResultTests
         stream.Position = 0;
         var responseDetails = JsonSerializer.Deserialize<ProblemDetails>(stream, JsonSerializerOptions.Web);
         Assert.Null(responseDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", responseDetails.Title);
+        Assert.Equal("Internal Server Error", responseDetails.Title);
         Assert.Equal(StatusCodes.Status500InternalServerError, responseDetails.Status);
     }
 
diff --git a/src/Http/Http.Results/test/ResultsTests.cs b/src/Http/Http.Results/test/ResultsTests.cs
index ce87ee10e9..e21d097b48 100644
--- a/src/Http/Http.Results/test/ResultsTests.cs
+++ b/src/Http/Http.Results/test/ResultsTests.cs
@@ -1349,7 +1349,7 @@ public partial class ResultsTests
         Assert.Null(result.ProblemDetails.Instance);
         Assert.Equal("application/problem+json", result.ContentType);
         Assert.Equal(StatusCodes.Status500InternalServerError, result.StatusCode);
-        Assert.Equal("An error occurred while processing your request.", result.ProblemDetails.Title);
+        Assert.Equal("Internal Server Error", result.ProblemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", result.ProblemDetails.Type);
         Assert.Empty(result.ProblemDetails.Extensions);
     }
diff --git a/src/Http/Http.Results/test/TypedResultsTests.cs b/src/Http/Http.Results/test/TypedResultsTests.cs
index acee20c4d1..cef21cda67 100644
--- a/src/Http/Http.Results/test/TypedResultsTests.cs
+++ b/src/Http/Http.Results/test/TypedResultsTests.cs
@@ -1141,7 +1141,7 @@ public partial class TypedResultsTests
         Assert.Null(result.ProblemDetails.Instance);
         Assert.Equal("application/problem+json", result.ContentType);
         Assert.Equal(StatusCodes.Status500InternalServerError, result.StatusCode);
-        Assert.Equal("An error occurred while processing your request.", result.ProblemDetails.Title);
+        Assert.Equal("Internal Server Error", result.ProblemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", result.ProblemDetails.Type);
         Assert.Empty(result.ProblemDetails.Extensions);
     }
diff --git a/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs b/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs
index fd502060bf..c9a97ed0f3 100644
--- a/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs
+++ b/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs
@@ -2475,7 +2475,7 @@ public class ControllerBaseTest
         var problemDetails = Assert.IsType<ProblemDetails>(badRequestResult.Value);
         Assert.Equal(500, actionResult.StatusCode);
         Assert.Equal(500, problemDetails.Status);
-        Assert.Equal("An error occurred while processing your request.", problemDetails.Title);
+        Assert.Equal("Internal Server Error", problemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", problemDetails.Type);
         Assert.Equal("some-trace", problemDetails.Extensions["traceId"]);
     }
@@ -2568,7 +2568,7 @@ public class ControllerBaseTest
                     },
                     [500] = new ClientErrorData
                     {
-                        Title = "An error occurred while processing your request.",
+                        Title = "Internal Server Error",
                         Link = "https://tools.ietf.org/html/rfc9110#section-15.6.1"
                     }
                 }
diff --git a/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs b/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs
index 2695b167ff..d8aa6ac0e8 100644
--- a/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs
+++ b/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs
@@ -20,7 +20,7 @@ public class ProblemDetailsFactoryTest
 
         // Assert
         Assert.Equal(500, problemDetails.Status);
-        Assert.Equal("An error occurred while processing your request.", problemDetails.Title);
+        Assert.Equal("Internal Server Error", problemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", problemDetails.Type);
         Assert.Null(problemDetails.Instance);
         Assert.Null(problemDetails.Detail);
diff --git a/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs b/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs
index 967c1aa486..b8d3a18fe2 100644
--- a/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs
+++ b/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs
@@ -133,7 +133,7 @@ internal static class ProblemDetailsDefaults
         [500] =
         (
             "https://tools.ietf.org/html/rfc9110#section-15.6.1",
-            "An error occurred while processing your request."
+            "Internal Server Error"
         ),
 
         [501] =

✅ Attempt 3: PASS

Attempt 3 — Model exploration

Approach: Same as attempt 0 — this is a string constant fix with only one correct value.
The 500 title must match RFC 9110: "Internal Server Error". There is no alternative approach.

📄 Diff

diff --git a/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs b/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs
index 2afabbec3f..b36499ee52 100644
--- a/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs
+++ b/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs
@@ -560,7 +560,7 @@ public partial class DefaultProblemDetailsWriterTest
         Assert.NotNull(problemDetails);
         Assert.Equal(StatusCodes.Status500InternalServerError, problemDetails.Status);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", problemDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", problemDetails.Title);
+        Assert.Equal("Internal Server Error", problemDetails.Title);
         Assert.Equal(expectedTraceId, problemDetails.Extensions["traceId"].ToString());
     }
 
diff --git a/src/Http/Http.Results/test/JsonResultTests.cs b/src/Http/Http.Results/test/JsonResultTests.cs
index 6e2b05dbcc..3af14f6f24 100644
--- a/src/Http/Http.Results/test/JsonResultTests.cs
+++ b/src/Http/Http.Results/test/JsonResultTests.cs
@@ -139,7 +139,7 @@ public class JsonResultTests
         stream.Position = 0;
         var responseDetails = JsonSerializer.Deserialize<ProblemDetails>(stream, JsonSerializerOptions.Web);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", responseDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", responseDetails.Title);
+        Assert.Equal("Internal Server Error", responseDetails.Title);
         Assert.Equal(StatusCodes.Status500InternalServerError, responseDetails.Status);
     }
 
diff --git a/src/Http/Http.Results/test/ProblemResultTests.cs b/src/Http/Http.Results/test/ProblemResultTests.cs
index c01c42a5d2..8e41555548 100644
--- a/src/Http/Http.Results/test/ProblemResultTests.cs
+++ b/src/Http/Http.Results/test/ProblemResultTests.cs
@@ -37,7 +37,7 @@ public class ProblemResultTests
         stream.Position = 0;
         var responseDetails = JsonSerializer.Deserialize<ProblemDetails>(stream, JsonSerializerOptions.Web);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", responseDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", responseDetails.Title);
+        Assert.Equal("Internal Server Error", responseDetails.Title);
         Assert.Equal(StatusCodes.Status500InternalServerError, responseDetails.Status);
     }
 
@@ -69,7 +69,7 @@ public class ProblemResultTests
         stream.Position = 0;
         var responseDetails = JsonSerializer.Deserialize<ProblemDetails>(stream, JsonSerializerOptions.Web);
         Assert.Null(responseDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", responseDetails.Title);
+        Assert.Equal("Internal Server Error", responseDetails.Title);
         Assert.Equal(StatusCodes.Status500InternalServerError, responseDetails.Status);
     }
 
diff --git a/src/Http/Http.Results/test/ResultsTests.cs b/src/Http/Http.Results/test/ResultsTests.cs
index ce87ee10e9..e21d097b48 100644
--- a/src/Http/Http.Results/test/ResultsTests.cs
+++ b/src/Http/Http.Results/test/ResultsTests.cs
@@ -1349,7 +1349,7 @@ public partial class ResultsTests
         Assert.Null(result.ProblemDetails.Instance);
         Assert.Equal("application/problem+json", result.ContentType);
         Assert.Equal(StatusCodes.Status500InternalServerError, result.StatusCode);
-        Assert.Equal("An error occurred while processing your request.", result.ProblemDetails.Title);
+        Assert.Equal("Internal Server Error", result.ProblemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", result.ProblemDetails.Type);
         Assert.Empty(result.ProblemDetails.Extensions);
     }
diff --git a/src/Http/Http.Results/test/TypedResultsTests.cs b/src/Http/Http.Results/test/TypedResultsTests.cs
index acee20c4d1..cef21cda67 100644
--- a/src/Http/Http.Results/test/TypedResultsTests.cs
+++ b/src/Http/Http.Results/test/TypedResultsTests.cs
@@ -1141,7 +1141,7 @@ public partial class TypedResultsTests
         Assert.Null(result.ProblemDetails.Instance);
         Assert.Equal("application/problem+json", result.ContentType);
         Assert.Equal(StatusCodes.Status500InternalServerError, result.StatusCode);
-        Assert.Equal("An error occurred while processing your request.", result.ProblemDetails.Title);
+        Assert.Equal("Internal Server Error", result.ProblemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", result.ProblemDetails.Type);
         Assert.Empty(result.ProblemDetails.Extensions);
     }
diff --git a/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs b/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs
index fd502060bf..c9a97ed0f3 100644
--- a/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs
+++ b/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs
@@ -2475,7 +2475,7 @@ public class ControllerBaseTest
         var problemDetails = Assert.IsType<ProblemDetails>(badRequestResult.Value);
         Assert.Equal(500, actionResult.StatusCode);
         Assert.Equal(500, problemDetails.Status);
-        Assert.Equal("An error occurred while processing your request.", problemDetails.Title);
+        Assert.Equal("Internal Server Error", problemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", problemDetails.Type);
         Assert.Equal("some-trace", problemDetails.Extensions["traceId"]);
     }
@@ -2568,7 +2568,7 @@ public class ControllerBaseTest
                     },
                     [500] = new ClientErrorData
                     {
-                        Title = "An error occurred while processing your request.",
+                        Title = "Internal Server Error",
                         Link = "https://tools.ietf.org/html/rfc9110#section-15.6.1"
                     }
                 }
diff --git a/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs b/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs
index 2695b167ff..d8aa6ac0e8 100644
--- a/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs
+++ b/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs
@@ -20,7 +20,7 @@ public class ProblemDetailsFactoryTest
 
         // Assert
         Assert.Equal(500, problemDetails.Status);
-        Assert.Equal("An error occurred while processing your request.", problemDetails.Title);
+        Assert.Equal("Internal Server Error", problemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", problemDetails.Type);
         Assert.Null(problemDetails.Instance);
         Assert.Null(problemDetails.Detail);
diff --git a/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs b/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs
index 967c1aa486..b8d3a18fe2 100644
--- a/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs
+++ b/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs
@@ -133,7 +133,7 @@ internal static class ProblemDetailsDefaults
         [500] =
         (
             "https://tools.ietf.org/html/rfc9110#section-15.6.1",
-            "An error occurred while processing your request."
+            "Internal Server Error"
         ),
 
         [501] =

✅ Attempt 4: PASS

Attempt 4 — Model exploration

Approach: Same as attempt 0 — this is a string constant fix with only one correct value.
The 500 title must match RFC 9110: "Internal Server Error". There is no alternative approach.

📄 Diff

diff --git a/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs b/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs
index 2afabbec3f..b36499ee52 100644
--- a/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs
+++ b/src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs
@@ -560,7 +560,7 @@ public partial class DefaultProblemDetailsWriterTest
         Assert.NotNull(problemDetails);
         Assert.Equal(StatusCodes.Status500InternalServerError, problemDetails.Status);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", problemDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", problemDetails.Title);
+        Assert.Equal("Internal Server Error", problemDetails.Title);
         Assert.Equal(expectedTraceId, problemDetails.Extensions["traceId"].ToString());
     }
 
diff --git a/src/Http/Http.Results/test/JsonResultTests.cs b/src/Http/Http.Results/test/JsonResultTests.cs
index 6e2b05dbcc..3af14f6f24 100644
--- a/src/Http/Http.Results/test/JsonResultTests.cs
+++ b/src/Http/Http.Results/test/JsonResultTests.cs
@@ -139,7 +139,7 @@ public class JsonResultTests
         stream.Position = 0;
         var responseDetails = JsonSerializer.Deserialize<ProblemDetails>(stream, JsonSerializerOptions.Web);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", responseDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", responseDetails.Title);
+        Assert.Equal("Internal Server Error", responseDetails.Title);
         Assert.Equal(StatusCodes.Status500InternalServerError, responseDetails.Status);
     }
 
diff --git a/src/Http/Http.Results/test/ProblemResultTests.cs b/src/Http/Http.Results/test/ProblemResultTests.cs
index c01c42a5d2..8e41555548 100644
--- a/src/Http/Http.Results/test/ProblemResultTests.cs
+++ b/src/Http/Http.Results/test/ProblemResultTests.cs
@@ -37,7 +37,7 @@ public class ProblemResultTests
         stream.Position = 0;
         var responseDetails = JsonSerializer.Deserialize<ProblemDetails>(stream, JsonSerializerOptions.Web);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", responseDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", responseDetails.Title);
+        Assert.Equal("Internal Server Error", responseDetails.Title);
         Assert.Equal(StatusCodes.Status500InternalServerError, responseDetails.Status);
     }
 
@@ -69,7 +69,7 @@ public class ProblemResultTests
         stream.Position = 0;
         var responseDetails = JsonSerializer.Deserialize<ProblemDetails>(stream, JsonSerializerOptions.Web);
         Assert.Null(responseDetails.Type);
-        Assert.Equal("An error occurred while processing your request.", responseDetails.Title);
+        Assert.Equal("Internal Server Error", responseDetails.Title);
         Assert.Equal(StatusCodes.Status500InternalServerError, responseDetails.Status);
     }
 
diff --git a/src/Http/Http.Results/test/ResultsTests.cs b/src/Http/Http.Results/test/ResultsTests.cs
index ce87ee10e9..e21d097b48 100644
--- a/src/Http/Http.Results/test/ResultsTests.cs
+++ b/src/Http/Http.Results/test/ResultsTests.cs
@@ -1349,7 +1349,7 @@ public partial class ResultsTests
         Assert.Null(result.ProblemDetails.Instance);
         Assert.Equal("application/problem+json", result.ContentType);
         Assert.Equal(StatusCodes.Status500InternalServerError, result.StatusCode);
-        Assert.Equal("An error occurred while processing your request.", result.ProblemDetails.Title);
+        Assert.Equal("Internal Server Error", result.ProblemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", result.ProblemDetails.Type);
         Assert.Empty(result.ProblemDetails.Extensions);
     }
diff --git a/src/Http/Http.Results/test/TypedResultsTests.cs b/src/Http/Http.Results/test/TypedResultsTests.cs
index acee20c4d1..cef21cda67 100644
--- a/src/Http/Http.Results/test/TypedResultsTests.cs
+++ b/src/Http/Http.Results/test/TypedResultsTests.cs
@@ -1141,7 +1141,7 @@ public partial class TypedResultsTests
         Assert.Null(result.ProblemDetails.Instance);
         Assert.Equal("application/problem+json", result.ContentType);
         Assert.Equal(StatusCodes.Status500InternalServerError, result.StatusCode);
-        Assert.Equal("An error occurred while processing your request.", result.ProblemDetails.Title);
+        Assert.Equal("Internal Server Error", result.ProblemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", result.ProblemDetails.Type);
         Assert.Empty(result.ProblemDetails.Extensions);
     }
diff --git a/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs b/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs
index fd502060bf..c9a97ed0f3 100644
--- a/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs
+++ b/src/Mvc/Mvc.Core/test/ControllerBaseTest.cs
@@ -2475,7 +2475,7 @@ public class ControllerBaseTest
         var problemDetails = Assert.IsType<ProblemDetails>(badRequestResult.Value);
         Assert.Equal(500, actionResult.StatusCode);
         Assert.Equal(500, problemDetails.Status);
-        Assert.Equal("An error occurred while processing your request.", problemDetails.Title);
+        Assert.Equal("Internal Server Error", problemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", problemDetails.Type);
         Assert.Equal("some-trace", problemDetails.Extensions["traceId"]);
     }
@@ -2568,7 +2568,7 @@ public class ControllerBaseTest
                     },
                     [500] = new ClientErrorData
                     {
-                        Title = "An error occurred while processing your request.",
+                        Title = "Internal Server Error",
                         Link = "https://tools.ietf.org/html/rfc9110#section-15.6.1"
                     }
                 }
diff --git a/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs b/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs
index 2695b167ff..d8aa6ac0e8 100644
--- a/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs
+++ b/src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs
@@ -20,7 +20,7 @@ public class ProblemDetailsFactoryTest
 
         // Assert
         Assert.Equal(500, problemDetails.Status);
-        Assert.Equal("An error occurred while processing your request.", problemDetails.Title);
+        Assert.Equal("Internal Server Error", problemDetails.Title);
         Assert.Equal("https://tools.ietf.org/html/rfc9110#section-15.6.1", problemDetails.Type);
         Assert.Null(problemDetails.Instance);
         Assert.Null(problemDetails.Detail);
diff --git a/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs b/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs
index 967c1aa486..b8d3a18fe2 100644
--- a/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs
+++ b/src/Shared/ProblemDetails/ProblemDetailsDefaults.cs
@@ -133,7 +133,7 @@ internal static class ProblemDetailsDefaults
         [500] =
         (
             "https://tools.ietf.org/html/rfc9110#section-15.6.1",
-            "An error occurred while processing your request."
+            "Internal Server Error"
         ),
 
         [501] =

Change the ProblemDetails default title for status 500 from 'An error occurred while processing your request.' to 'Internal Server Error' to match RFC 9110 and ReasonPhrases.GetReasonPhrase(500). All other status codes already use the RFC-standard reason phrase as their title. Fixes dotnet#16880 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

dotnet-policy-service · 2026-03-01T18:08:47Z

Thanks for your PR, @@kubaflo. Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

Copilot

Pull request overview

Aligns the default ProblemDetails title for HTTP 500 with the RFC 9110 reason phrase to keep ProblemDetailsDefaults consistent with ReasonPhrases.GetReasonPhrase(500) and the other default mappings.

Changes:

Updated the 500 default title in ProblemDetailsDefaults to "Internal Server Error".
Updated affected unit tests to assert the new 500 title across MVC, Http.Results, and Http.Extensions.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/Shared/ProblemDetails/ProblemDetailsDefaults.cs	Changes the default 500 `ProblemDetails` title to the RFC 9110 reason phrase.
src/Mvc/Mvc.Core/test/Infrastructure/ProblemDetailsFactoryTest.cs	Updates default 500 title assertion.
src/Mvc/Mvc.Core/test/ControllerBaseTest.cs	Updates `Problem()` and `ClientErrorMapping[500]` title assertions.
src/Http/Http.Results/test/TypedResultsTests.cs	Updates 500 problem result title assertion.
src/Http/Http.Results/test/ResultsTests.cs	Updates 500 problem result title assertion.
src/Http/Http.Results/test/ProblemResultTests.cs	Updates 500 problem JSON title assertions.
src/Http/Http.Results/test/JsonResultTests.cs	Updates 500 problem JSON title assertion.
src/Http/Http.Extensions/test/ProblemDetailsDefaultWriterTest.cs	Updates default writer 500 title assertion.

mikekistler

This looks good to me and it addresses a long outstanding issue. 👍

Copilot AI review requested due to automatic review settings March 1, 2026 18:08

kubaflo requested review from a team, BrennanConroy and halter73 as code owners March 1, 2026 18:08

github-actions bot added the area-networking Includes servers, yarp, json patch, bedrock, websockets, http client factory, and http abstractions label Mar 1, 2026

dotnet-policy-service bot added the community-contribution Indicates that the PR has been added by a community member label Mar 1, 2026

Copilot started reviewing on behalf of kubaflo March 1, 2026 18:08 View session

Copilot AI reviewed Mar 1, 2026

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build-analysis bot mentioned this pull request Mar 1, 2026

Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. dotnet/dnceng#5922

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mikekistler approved these changes Mar 2, 2026

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Fix ClientErrorMapping 500 title to match RFC 9110#65590

Fix ClientErrorMapping 500 title to match RFC 9110#65590
kubaflo wants to merge 1 commit intodotnet:mainfrom
kubaflo:fix/client-error-mapping-500-title-16880

kubaflo commented Mar 1, 2026 •

edited

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kubaflo commented Mar 1, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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🤖 AI Summary

Key Findings

Fix Approach

Test Command

Test Result: ✅ TESTS UPDATED

Gate Result: ✅ PASSED

Fix Exploration Summary

Attempt Results

Cross-Pollination

Recommendation

Attempt 0 — Baseline (claude-opus-4.6-fast)

Attempt 1 — Model exploration

Attempt 2 — Model exploration

Attempt 3 — Model exploration

Attempt 4 — Model exploration

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kubaflo commented Mar 1, 2026 •

edited

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