Support DisplayNameAttribute for name resolution in AI libraries

src/Libraries/Microsoft.Extensions.AI.Abstractions/ChatCompletion/ChatResponseFormat.cs

@@ -88,7 +88,7 @@ public static ChatResponseFormatJson ForJsonSchema(
 
         return ForJsonSchema(
             schema,
-            schemaName ?? InvalidNameCharsRegex().Replace(schemaType.Name, "_"),
+            schemaName ?? schemaType.GetCustomAttribute<DisplayNameAttribute>()?.DisplayName ?? InvalidNameCharsRegex().Replace(schemaType.Name, "_"),
             schemaDescription ?? schemaType.GetCustomAttribute<DescriptionAttribute>()?.Description);
     }
 

src/Libraries/Microsoft.Extensions.AI.Abstractions/Functions/AIFunctionFactory.cs

@@ -729,7 +729,7 @@ private ReflectionAIFunctionDescriptor(DescriptorKey key, JsonSerializerOptions
 
             ReturnParameterMarshaller = GetReturnParameterMarshaller(key, serializerOptions, out Type? returnType);
             Method = key.Method;
-            Name = key.Name ?? GetFunctionName(key.Method);
+            Name = key.Name ?? key.Method.GetCustomAttribute<DisplayNameAttribute>(inherit: true)?.DisplayName ?? GetFunctionName(key.Method);
             Description = key.Description ?? key.Method.GetCustomAttribute<DescriptionAttribute>(inherit: true)?.Description ?? string.Empty;
             JsonSerializerOptions = serializerOptions;
             ReturnJsonSchema = returnType is null || key.ExcludeResultSchema ? null : AIJsonUtilities.CreateJsonSchema(

src/Libraries/Microsoft.Extensions.AI.Abstractions/Utilities/AIJsonUtilities.Schema.Create.cs

@@ -80,7 +80,7 @@ public static JsonElement CreateFunctionJsonSchema(
 
         serializerOptions ??= DefaultOptions;
         inferenceOptions ??= AIJsonSchemaCreateOptions.Default;
-        title ??= method.Name;
+        title ??= method.GetCustomAttribute<DisplayNameAttribute>()?.DisplayName ?? method.Name;
         description ??= method.GetCustomAttribute<DescriptionAttribute>()?.Description;
 
         JsonObject parameterSchemas = new();

test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/ChatCompletion/ChatResponseFormatTests.cs

@@ -169,6 +169,34 @@ public void ForJsonSchema_ComplexType_Succeeds(bool generic, string? name, strin
         Assert.Equal(description ?? "abcd", format.SchemaDescription);
     }
 
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public void ForJsonSchema_DisplayNameAttribute_UsedForSchemaName(bool generic)
+    {
+        ChatResponseFormatJson format = generic ?
+            ChatResponseFormat.ForJsonSchema<TypeWithDisplayName>(TestJsonSerializerContext.Default.Options) :
+            ChatResponseFormat.ForJsonSchema(typeof(TypeWithDisplayName), TestJsonSerializerContext.Default.Options);
+
+        Assert.NotNull(format);
+        Assert.NotNull(format.Schema);
+        Assert.Equal("custom_type_name", format.SchemaName);
+        Assert.Equal("Type description", format.SchemaDescription);
+    }
+
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public void ForJsonSchema_DisplayNameAttribute_CanBeOverridden(bool generic)
+    {
+        ChatResponseFormatJson format = generic ?
+            ChatResponseFormat.ForJsonSchema<TypeWithDisplayName>(TestJsonSerializerContext.Default.Options, schemaName: "override_name") :
+            ChatResponseFormat.ForJsonSchema(typeof(TypeWithDisplayName), TestJsonSerializerContext.Default.Options, schemaName: "override_name");
+
+        Assert.NotNull(format);
+        Assert.Equal("override_name", format.SchemaName);
+    }
+
     [Description("abcd")]
     public class SomeType
     {
@@ -178,4 +206,11 @@ public class SomeType
         [Description("hijk")]
         public string? SomeString { get; set; }
     }
+
+    [DisplayName("custom_type_name")]
+    [Description("Type description")]
+    public class TypeWithDisplayName
+    {
+        public int Value { get; set; }
+    }
 }

test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/TestJsonSerializerContext.cs

@@ -37,5 +37,6 @@ namespace Microsoft.Extensions.AI;
 [JsonSerializable(typeof(decimal))] // Used in Content tests
 [JsonSerializable(typeof(HostedMcpServerToolApprovalMode))]
 [JsonSerializable(typeof(ChatResponseFormatTests.SomeType))]
+[JsonSerializable(typeof(ChatResponseFormatTests.TypeWithDisplayName))]
 [JsonSerializable(typeof(ResponseContinuationToken))]
 internal sealed partial class TestJsonSerializerContext : JsonSerializerContext;

test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/Utilities/AIJsonUtilitiesTests.cs

@@ -423,6 +423,41 @@
         AssertDeepEquals(expectedSchema.RootElement, func.JsonSchema);
     }
 
+    [Fact]
+    public static void CreateFunctionJsonSchema_DisplayNameAttribute_UsedForTitle()
+    {
+        [DisplayName("custom_method_name")]
+        [Description("Method description")]
+        static void TestMethod(int x, int y)
+        {
+        }
+
+        var method = ((Action<int, int>)TestMethod).Method;
+        JsonElement schema = AIJsonUtilities.CreateFunctionJsonSchema(method);
+
+        using JsonDocument doc = JsonDocument.Parse(schema.GetRawText());
+        Assert.True(doc.RootElement.TryGetProperty("title", out JsonElement titleElement));
+        Assert.Equal("custom_method_name", titleElement.GetString());
+        Assert.True(doc.RootElement.TryGetProperty("description", out JsonElement descElement));
+        Assert.Equal("Method description", descElement.GetString());
+    }
+
+    [Fact]
+    public static void CreateFunctionJsonSchema_DisplayNameAttribute_CanBeOverridden()
+    {
+        [DisplayName("custom_method_name")]
+        static void TestMethod()
+        {
+        }
+
+        var method = ((Action)TestMethod).Method;
+        JsonElement schema = AIJsonUtilities.CreateFunctionJsonSchema(method, title: "override_title");
+
+        using JsonDocument doc = JsonDocument.Parse(schema.GetRawText());
+        Assert.True(doc.RootElement.TryGetProperty("title", out JsonElement titleElement));
+        Assert.Equal("override_title", titleElement.GetString());
+    }
+
     [Fact]
     public static void CreateJsonSchema_CanBeBoolean()
     {

test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs

@@ -237,6 +237,39 @@ public void Metadata_DerivedFromLambda()
             p => Assert.Equal("This is B", p.GetCustomAttribute<DescriptionAttribute>()?.Description));
     }
 
+    [Fact]
+    public void Metadata_DisplayNameAttribute()
+    {
+        // Test DisplayNameAttribute on a delegate method
+        Func<string> funcWithDisplayName = [DisplayName("get_user_id")] () => "test";
+        AIFunction func = AIFunctionFactory.Create(funcWithDisplayName);
+        Assert.Equal("get_user_id", func.Name);
+        Assert.Empty(func.Description);
+
+        // Test DisplayNameAttribute with DescriptionAttribute
+        Func<string> funcWithBoth = [DisplayName("my_function")][Description("A test function")] () => "test";
+        func = AIFunctionFactory.Create(funcWithBoth);
+        Assert.Equal("my_function", func.Name);
+        Assert.Equal("A test function", func.Description);
+
+        // Test that explicit name parameter takes precedence over DisplayNameAttribute
+        func = AIFunctionFactory.Create(funcWithDisplayName, name: "explicit_name");
+        Assert.Equal("explicit_name", func.Name);
+
+        // Test DisplayNameAttribute with options
+        func = AIFunctionFactory.Create(funcWithDisplayName, new AIFunctionFactoryOptions());
+        Assert.Equal("get_user_id", func.Name);
+
+        // Test that options.Name takes precedence over DisplayNameAttribute
+        func = AIFunctionFactory.Create(funcWithDisplayName, new AIFunctionFactoryOptions { Name = "options_name" });
+        Assert.Equal("options_name", func.Name);
+
+        // Test function without DisplayNameAttribute falls back to method name
+        Func<string> funcWithoutDisplayName = () => "test";
+        func = AIFunctionFactory.Create(funcWithoutDisplayName);
+        Assert.Contains("Metadata_DisplayNameAttribute", func.Name); // Will contain the lambda method name
+    }
+
     [Fact]
     public void AIFunctionFactoryCreateOptions_ValuesPropagateToAIFunction()
     {