Remove LegacyTitledEnumSchema obsolete API

BREAKING CHANGE: Removed the [Obsolete] LegacyTitledEnumSchema API and related Obsoletions constants. The LegacyTitledEnumSchema class used enumNames for titled enums and has been replaced by TitledSingleSelectEnumSchema using oneOf with const/title. JSON with enumNames will now deserialize as UntitledSingleSelectEnumSchema (ignoring enumNames).

- Removed LegacyTitledEnumSchema class from ElicitRequestParams.cs
- Removed LegacyTitledEnumSchema from JSON converter (deserialization now ignores enumNames)
- Removed LegacyTitledEnumSchema from GetDefaultAsJsonElement method
- Removed obsoletions constants and added comment that MCP9001 cannot be reused
- Removed LegacyTitledEnumSchema tests from EnumSchemaTests.cs
- Removed LegacyTitledEnumSchema tests from ElicitationDefaultValuesTests.cs
- Removed LegacyTitledEnumSchema tests from PrimitiveSchemaDefinitionTests.cs
- Removed LegacyTitledEnumSchema usage from ConformanceTools.cs
- Updated documentation in elicitation.md
- Updated XML documentation comments to remove references

Co-authored-by: jeffhandley <1031940+jeffhandley@users.noreply.github.com>

Author: Copilot

docs/concepts/elicitation/elicitation.md

@@ -32,7 +32,6 @@ For enum types, the SDK supports several schema formats:
 - **TitledSingleSelectEnumSchema**: A single-select enum with separate display titles for each option (using JSON Schema `oneOf` with `const` and `title`).
 - **UntitledMultiSelectEnumSchema**: A multi-select enum allowing multiple values to be selected.
 - **TitledMultiSelectEnumSchema**: A multi-select enum with display titles for each option.
-- **LegacyTitledEnumSchema** (deprecated): The legacy enum schema using `enumNames` for backward compatibility.
 
 The server can request a single input or multiple inputs at once.
 To help distinguish multiple inputs, each input has a unique name.

src/Common/Obsoletions.cs

@@ -19,7 +19,5 @@ namespace ModelContextProtocol;
 /// </remarks>
 internal static class Obsoletions
 {
-    public const string LegacyTitledEnumSchema_DiagnosticId = "MCP9001";
-    public const string LegacyTitledEnumSchema_Message = "The EnumSchema and LegacyTitledEnumSchema APIs are deprecated as of specification version 2025-11-25 and will be removed in a future major version. See SEP-1330 for more information.";
-    public const string LegacyTitledEnumSchema_Url = "https://github.com/modelcontextprotocol/modelcontextprotocol/issues/1330";
+    // MCP9001 was used for LegacyTitledEnumSchema (removed) - do not reuse
 }

src/ModelContextProtocol.Core/Protocol/ElicitRequestParams.cs

@@ -86,8 +86,7 @@ public string Mode
     /// <value>
     /// Possible values are <see cref="StringSchema"/>, <see cref="NumberSchema"/>, <see cref="BooleanSchema"/>,
     /// <see cref="UntitledSingleSelectEnumSchema"/>, <see cref="TitledSingleSelectEnumSchema"/>,
-    /// <see cref="UntitledMultiSelectEnumSchema"/>, <see cref="TitledMultiSelectEnumSchema"/>,
-    /// and <see cref="LegacyTitledEnumSchema"/> (deprecated).
+    /// <see cref="UntitledMultiSelectEnumSchema"/>, and <see cref="TitledMultiSelectEnumSchema"/>.
     /// </value>
     [JsonPropertyName("requestedSchema")]
     public RequestSchema? RequestedSchema { get; set; }
@@ -132,8 +131,7 @@ public IDictionary<string, PrimitiveSchemaDefinition> Properties
     /// Represents a restricted subset of JSON Schema:
     /// <see cref="StringSchema"/>, <see cref="NumberSchema"/>, <see cref="BooleanSchema"/>,
     /// <see cref="UntitledSingleSelectEnumSchema"/>, <see cref="TitledSingleSelectEnumSchema"/>,
-    /// <see cref="UntitledMultiSelectEnumSchema"/>, <see cref="TitledMultiSelectEnumSchema"/>,
-    /// or <see cref="LegacyTitledEnumSchema"/> (deprecated).
+    /// <see cref="UntitledMultiSelectEnumSchema"/>, or <see cref="TitledMultiSelectEnumSchema"/>.
     /// </summary>
     [JsonConverter(typeof(Converter))]
     public abstract class PrimitiveSchemaDefinition
@@ -153,9 +151,6 @@ protected private PrimitiveSchemaDefinition()
             TitledSingleSelectEnumSchema { Default: { } s } => JsonSerializer.SerializeToElement(s, McpJsonUtilities.JsonContext.Default.String),
             UntitledMultiSelectEnumSchema { Default: { } a } => JsonSerializer.SerializeToElement(a, McpJsonUtilities.JsonContext.Default.IListString),
             TitledMultiSelectEnumSchema { Default: { } a } => JsonSerializer.SerializeToElement(a, McpJsonUtilities.JsonContext.Default.IListString),
-#pragma warning disable MCP9001 // LegacyTitledEnumSchema is deprecated but supported for backward compatibility
-            LegacyTitledEnumSchema { Default: { } s } => JsonSerializer.SerializeToElement(s, McpJsonUtilities.JsonContext.Default.String),
-#pragma warning restore MCP9001
             _ => null,
         };
 
@@ -329,27 +324,12 @@ public sealed class Converter : JsonConverter<PrimitiveSchemaDefinition>
                         }
                         else if (enumValues is not null)
                         {
-                            if (enumNames is not null)
+                            // UntitledSingleSelectEnumSchema (enumNames is ignored if present)
+                            psd = new UntitledSingleSelectEnumSchema
                             {
-                                // LegacyTitledEnumSchema is deprecated but supported for backward compatibility.
-#pragma warning disable MCP9001
-                                psd = new LegacyTitledEnumSchema
-#pragma warning restore MCP9001
-                                {
-                                    Enum = enumValues,
-                                    EnumNames = enumNames,
-                                    Default = defaultString,
-                                };
-                            }
-                            else
-                            {
-                                // UntitledSingleSelectEnumSchema
-                                psd = new UntitledSingleSelectEnumSchema
-                                {
-                                    Enum = enumValues,
-                                    Default = defaultString,
-                                };
-                            }
+                                Enum = enumValues,
+                                Default = defaultString,
+                            };
                         }
                         else
                         {
@@ -642,25 +622,6 @@ public override void Write(Utf8JsonWriter writer, PrimitiveSchemaDefinition valu
                         }
                         break;
 
-#pragma warning disable MCP9001 // LegacyTitledEnumSchema is deprecated but supported for backward compatibility
-                    case LegacyTitledEnumSchema legacyTitledEnum:
-#pragma warning restore MCP9001
-                        if (legacyTitledEnum.Enum is not null)
-                        {
-                            writer.WritePropertyName("enum");
-                            JsonSerializer.Serialize(writer, legacyTitledEnum.Enum, McpJsonUtilities.JsonContext.Default.IListString);
-                        }
-                        if (legacyTitledEnum.EnumNames is not null)
-                        {
-                            writer.WritePropertyName("enumNames");
-                            JsonSerializer.Serialize(writer, legacyTitledEnum.EnumNames, McpJsonUtilities.JsonContext.Default.IListString);
-                        }
-                        if (legacyTitledEnum.Default is not null)
-                        {
-                            writer.WriteString("default", legacyTitledEnum.Default);
-                        }
-                        break;
-
                     default:
                         throw new JsonException($"Unexpected schema type: {value.GetType().Name}");
                 }
@@ -1008,48 +969,4 @@ public override string Type
         public IList<string>? Default { get; set; }
     }
 
-    /// <summary>
-    /// Represents a legacy schema for an enum type with enumNames.
-    /// </summary>
-    /// <remarks>
-    /// This schema is deprecated in favor of <see cref="TitledSingleSelectEnumSchema"/>.
-    /// </remarks>
-    [Obsolete(Obsoletions.LegacyTitledEnumSchema_Message, DiagnosticId = Obsoletions.LegacyTitledEnumSchema_DiagnosticId, UrlFormat = Obsoletions.LegacyTitledEnumSchema_Url)]
-    public sealed class LegacyTitledEnumSchema : PrimitiveSchemaDefinition
-    {
-        /// <inheritdoc/>
-        [JsonPropertyName("type")]
-        public override string Type
-        {
-            get => "string";
-            set
-            {
-                if (value is not "string")
-                {
-                    throw new ArgumentException("Type must be 'string'.", nameof(value));
-                }
-            }
-        }
-
-        /// <summary>Gets or sets the list of allowed string values for the enum.</summary>
-        [JsonPropertyName("enum")]
-        [field: MaybeNull]
-        public IList<string> Enum
-        {
-            get => field ??= [];
-            set
-            {
-                Throw.IfNull(value);
-                field = value;
-            }
-        }
-
-        /// <summary>Gets or sets optional display names corresponding to the enum values.</summary>
-        [JsonPropertyName("enumNames")]
-        public IList<string>? EnumNames { get; set; }
-
-        /// <summary>Gets or sets the default value for the enum.</summary>
-        [JsonPropertyName("default")]
-        public string? Default { get; set; }
-    }
 }

tests/ModelContextProtocol.ConformanceServer/Tools/ConformanceTools.cs

@@ -346,14 +346,6 @@ public static async Task<string> ElicitationSep1330Enums(
                             new() { Const = "value3", Title = "Third Option" }
                         ]
                     },
-#pragma warning disable MCP9001
-                    ["legacyEnum"] = new ElicitRequestParams.LegacyTitledEnumSchema()
-                    {
-                        Description = "Choose a legacy option",
-                        Enum = ["opt1", "opt2", "opt3"],
-                        EnumNames = ["Option One", "Option Two", "Option Three"]
-                    },
-#pragma warning restore MCP9001
                     ["untitledMulti"] = new ElicitRequestParams.UntitledMultiSelectEnumSchema()
                     {
                         Description = "Choose multiple options",

tests/ModelContextProtocol.Tests/Protocol/ElicitationDefaultValuesTests.cs

@@ -282,26 +282,6 @@ public static void TitledMultiSelectEnumSchema_Default_Null_DoesNotSerialize()
         Assert.DoesNotContain("\"default\"", json);
     }
 
-#pragma warning disable MCP9001 // LegacyTitledEnumSchema is deprecated but supported for backward compatibility
-    [Fact]
-    public static void LegacyTitledEnumSchema_Default_Null_DoesNotSerialize()
-    {
-        // Arrange
-        var schema = new ElicitRequestParams.LegacyTitledEnumSchema
-        {
-            Title = "Legacy Options",
-            Enum = ["option1", "option2"],
-            EnumNames = ["Option 1", "Option 2"]
-        };
-
-        // Act - serialize as base type to use the converter
-        string json = JsonSerializer.Serialize<ElicitRequestParams.PrimitiveSchemaDefinition>(schema, McpJsonUtilities.DefaultOptions);
-
-        // Assert
-        Assert.DoesNotContain("\"default\"", json);
-    }
-#pragma warning restore MCP9001
-
     [Fact]
     public static void RequestSchema_WithAllDefaultTypes_Serializes_Correctly()
     {

tests/ModelContextProtocol.Tests/Protocol/EnumSchemaTests.cs

@@ -277,92 +277,4 @@ public void MultiSelectEnum_WithAnyOf_Deserializes_As_TitledMultiSelect()
         Assert.Equal("Administrator", result.Items.AnyOf[0].Title);
         Assert.Equal(["user"], result.Default);
     }
-
-#pragma warning disable MCP9001 // EnumSchema and LegacyTitledEnumSchema are deprecated but supported for backward compatibility
-    [Fact]
-    public void LegacyTitledEnumSchema_Serializes_Correctly()
-    {
-        // Arrange
-        var schema = new ElicitRequestParams.LegacyTitledEnumSchema
-        {
-            Title = "Environment",
-            Description = "Deployment environment",
-            Enum = ["dev", "staging", "prod"],
-            EnumNames = ["Development", "Staging", "Production"],
-            Default = "staging"
-        };
-
-        // Act
-        string json = JsonSerializer.Serialize<ElicitRequestParams.PrimitiveSchemaDefinition>(schema, McpJsonUtilities.DefaultOptions);
-        var deserialized = JsonSerializer.Deserialize<ElicitRequestParams.PrimitiveSchemaDefinition>(json, McpJsonUtilities.DefaultOptions);
-
-        // Assert
-        Assert.NotNull(deserialized);
-        var result = Assert.IsType<ElicitRequestParams.LegacyTitledEnumSchema>(deserialized);
-        Assert.Equal("string", result.Type);
-        Assert.Equal("Environment", result.Title);
-        Assert.Equal("Deployment environment", result.Description);
-        Assert.Equal(["dev", "staging", "prod"], result.Enum);
-        Assert.Equal(["Development", "Staging", "Production"], result.EnumNames);
-        Assert.Equal("staging", result.Default);
-        Assert.Contains("\"enumNames\":[\"Development\",\"Staging\",\"Production\"]", json);
-    }
-
-    [Fact]
-    public void LegacyTitledEnumSchema_Direct_Serializes_Correctly()
-    {
-        // Arrange
-        var schema = new ElicitRequestParams.LegacyTitledEnumSchema
-        {
-            Title = "Environment",
-            Description = "Deployment environment",
-            Enum = ["dev", "staging", "prod"],
-            EnumNames = ["Development", "Staging", "Production"],
-            Default = "staging"
-        };
-
-        // Act
-        string json = JsonSerializer.Serialize<ElicitRequestParams.PrimitiveSchemaDefinition>(schema, McpJsonUtilities.DefaultOptions);
-        var deserialized = JsonSerializer.Deserialize<ElicitRequestParams.PrimitiveSchemaDefinition>(json, McpJsonUtilities.DefaultOptions);
-
-        // Assert
-        Assert.NotNull(deserialized);
-        var result = Assert.IsType<ElicitRequestParams.LegacyTitledEnumSchema>(deserialized);
-        Assert.Equal("string", result.Type);
-        Assert.Equal("Environment", result.Title);
-        Assert.Equal("Deployment environment", result.Description);
-        Assert.Equal(["dev", "staging", "prod"], result.Enum);
-        Assert.Equal(["Development", "Staging", "Production"], result.EnumNames);
-        Assert.Equal("staging", result.Default);
-        Assert.Contains("\"enumNames\":[\"Development\",\"Staging\",\"Production\"]", json);
-    }
-
-    [Fact]
-    public void Enum_WithEnumNames_Deserializes_As_LegacyTitledEnumSchema()
-    {
-        // Arrange - JSON with enumNames should deserialize as (deprecated) LegacyTitledEnumSchema
-        string json = """
-            {
-                "type": "string",
-                "title": "Environment",
-                "description": "Deployment environment",
-                "enum": ["dev", "staging", "prod"],
-                "enumNames": ["Development", "Staging", "Production"],
-                "default": "staging"
-            }
-            """;
-        // Act
-        var deserialized = JsonSerializer.Deserialize<ElicitRequestParams.PrimitiveSchemaDefinition>(json, McpJsonUtilities.DefaultOptions);
-
-        // Assert
-        Assert.NotNull(deserialized);
-        var result = Assert.IsType<ElicitRequestParams.LegacyTitledEnumSchema>(deserialized);
-        Assert.Equal("string", result.Type);
-        Assert.Equal("Environment", result.Title);
-        Assert.Equal("Deployment environment", result.Description);
-        Assert.Equal(["dev", "staging", "prod"], result.Enum);
-        Assert.Equal(["Development", "Staging", "Production"], result.EnumNames);
-        Assert.Equal("staging", result.Default);
-    }
-#pragma warning restore MCP9001
 }

tests/ModelContextProtocol.Tests/Protocol/PrimitiveSchemaDefinitionTests.cs

@@ -257,39 +257,4 @@ public static void TitledMultiSelectEnumSchema_UnknownProperties_AreIgnored()
         Assert.Contains("optionX", enumSchema.Default);
         Assert.Contains("optionZ", enumSchema.Default);
     }
-
-#pragma warning disable MCP9001 // LegacyTitledEnumSchema is deprecated but supported for backward compatibility
-    [Fact]
-    public static void LegacyTitledEnumSchema_UnknownProperties_AreIgnored()
-    {
-        const string json = """
-        {
-            "type": "string",
-            "enum": ["option1", "option2"],
-
-            "unknownNull": null,
-            "unknownEmptyObject": {},
-            "unknownObject": {"a": 1},
-            "unknownEmptyArray": [],
-            "unknownArray": [1, 2, 3],
-            "unknownNestedObject": {"b": {"c": "d", "e": ["f"]}},
-
-            "enumNames": ["Option 1", "Option 2"],
-            "default": "option2"
-        }
-        """;
-
-        var result = JsonSerializer.Deserialize<ElicitRequestParams.PrimitiveSchemaDefinition>(
-            json,
-            McpJsonUtilities.DefaultOptions);
-        Assert.NotNull(result);
-        var enumSchema = Assert.IsType<ElicitRequestParams.LegacyTitledEnumSchema>(result);
-        Assert.Equal("string", enumSchema.Type);
-        Assert.Equal(2, enumSchema.Enum.Count);
-        Assert.Contains("option1", enumSchema.Enum);
-        Assert.Contains("option2", enumSchema.Enum);
-        Assert.Contains("Option 1", enumSchema.EnumNames!);
-        Assert.Contains("Option 2", enumSchema.EnumNames!);
-    }
-#pragma warning restore MCP9001
 }