Add an AIJsonSchemaTransformOptions property inside AIJsonSchemaCreateOptions and mark redundant properties in the latter as obsolete.

src/Libraries/Microsoft.Extensions.AI.Abstractions/Utilities/AIJsonSchemaCreateOptions.cs

@@ -38,22 +38,33 @@ public sealed record class AIJsonSchemaCreateOptions
     public Func<ParameterInfo, bool>? IncludeParameter { get; init; }
 
     /// <summary>
-    /// Gets a value indicating whether to include the type keyword in inferred schemas for .NET enums.
+    /// Gets a <see cref="AIJsonSchemaTransformOptions"/> governing transformations on the JSON schema after it has been generated.
     /// </summary>
+    public AIJsonSchemaTransformOptions? TransformOptions { get; init; }
+
+    /// <summary>
+    /// Gets a value indicating whether to include the type keyword in created schemas for .NET enums.
+    /// </summary>
+    [Obsolete("This property has been deprecated.")]
+    [System.ComponentModel.EditorBrowsable(System.ComponentModel.EditorBrowsableState.Never)]
     public bool IncludeTypeInEnumSchemas { get; init; } = true;
 
     /// <summary>
     /// Gets a value indicating whether to generate schemas with the additionalProperties set to false for .NET objects.
     /// </summary>
-    public bool DisallowAdditionalProperties { get; init; } = true;
+    [Obsolete("This property has been deprecated. Use the equivalent property in TransformOptions instead.")]
+    [System.ComponentModel.EditorBrowsable(System.ComponentModel.EditorBrowsableState.Never)]
+    public bool DisallowAdditionalProperties { get; init; }
 
     /// <summary>
-    /// Gets a value indicating whether to include the $schema keyword in inferred schemas.
+    /// Gets a value indicating whether to include the $schema keyword in created schemas.
     /// </summary>
     public bool IncludeSchemaKeyword { get; init; }
 
     /// <summary>
     /// Gets a value indicating whether to mark all properties as required in the schema.
     /// </summary>
+    [Obsolete("This property has been deprecated. Use the equivalent property in TransformOptions instead.")]
+    [System.ComponentModel.EditorBrowsable(System.ComponentModel.EditorBrowsableState.Never)]
     public bool RequireAllProperties { get; init; }
 }

src/Libraries/Microsoft.Extensions.AI.Abstractions/Utilities/AIJsonSchemaTransformOptions.cs

@@ -38,6 +38,11 @@ public sealed record class AIJsonSchemaTransformOptions
     /// </summary>
     public bool UseNullableKeyword { get; init; }
 
+    /// <summary>
+    /// Gets a value indicating whether to move the default keyword to the description field in the schema.
+    /// </summary>
+    public bool MoveDefaultKeywordToDescription { get; init; }
+
     /// <summary>
     /// Gets the default options instance.
     /// </summary>

src/Libraries/Microsoft.Extensions.AI.Abstractions/Utilities/AIJsonUtilities.Defaults.cs

@@ -116,4 +116,11 @@ private static JsonSerializerOptions CreateDefaultOptions()
     [JsonSerializable(typeof(AIFunctionArguments))]
     [EditorBrowsable(EditorBrowsableState.Never)] // Never use JsonContext directly, use DefaultOptions instead.
     private sealed partial class JsonContext : JsonSerializerContext;
+
+    [JsonSourceGenerationOptions(JsonSerializerDefaults.Web,
+        UseStringEnumConverter = true,
+        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
+        WriteIndented = false)]
+    [JsonSerializable(typeof(JsonNode))]
+    private sealed partial class JsonContextNoIndentation : JsonSerializerContext;
 }

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

@@ -5,7 +5,6 @@
 using System.ComponentModel;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
-using System.Linq;
 using System.Reflection;
 using System.Runtime.CompilerServices;
 using System.Text.Json;
@@ -40,7 +39,7 @@ public static partial class AIJsonUtilities
     private const string DefaultPropertyName = "default";
     private const string RefPropertyName = "$ref";
 
-    /// <summary>The uri used when populating the $schema keyword in inferred schemas.</summary>
+    /// <summary>The uri used when populating the $schema keyword in created schemas.</summary>
     private const string SchemaKeywordUri = "https://json-schema.org/draft/2020-12/schema";
 
     // List of keywords used by JsonSchemaExporter but explicitly disallowed by some AI vendors.
@@ -54,7 +53,7 @@ public static partial class AIJsonUtilities
     /// <param name="title">The title keyword used by the method schema.</param>
     /// <param name="description">The description keyword used by the method schema.</param>
     /// <param name="serializerOptions">The options used to extract the schema from the specified type.</param>
-    /// <param name="inferenceOptions">The options controlling schema inference.</param>
+    /// <param name="inferenceOptions">The options controlling schema creation.</param>
     /// <returns>A JSON schema document encoded as a <see cref="JsonElement"/>.</returns>
     /// <exception cref="ArgumentNullException"><paramref name="method"/> is <see langword="null"/>.</exception>
     public static JsonElement CreateFunctionJsonSchema(
@@ -106,13 +105,13 @@ public static JsonElement CreateFunctionJsonSchema(
                 inferenceOptions);
 
             parameterSchemas.Add(parameter.Name, parameterSchema);
-            if (!parameter.IsOptional || inferenceOptions.RequireAllProperties)
+            if (!parameter.IsOptional)
             {
                 (requiredProperties ??= []).Add((JsonNode)parameter.Name);
             }
         }
 
-        JsonObject schema = new();
+        JsonNode schema = new JsonObject();
         if (inferenceOptions.IncludeSchemaKeyword)
         {
             schema[SchemaPropertyName] = SchemaKeywordUri;
@@ -136,7 +135,13 @@ public static JsonElement CreateFunctionJsonSchema(
             schema[RequiredPropertyName] = requiredProperties;
         }
 
-        return JsonSerializer.SerializeToElement(schema, JsonContext.Default.JsonNode);
+        // Finally, apply any schema transformations if specified.
+        if (inferenceOptions.TransformOptions is { } options)
+        {
+            schema = TransformSchema(schema, options);
+        }
+
+        return JsonSerializer.SerializeToElement(schema, JsonContextNoIndentation.Default.JsonNode);
     }
 
     /// <summary>Creates a JSON schema for the specified type.</summary>
@@ -145,7 +150,7 @@ public static JsonElement CreateFunctionJsonSchema(
     /// <param name="hasDefaultValue"><see langword="true"/> if the parameter is optional; otherwise, <see langword="false"/>.</param>
     /// <param name="defaultValue">The default value of the optional parameter, if applicable.</param>
     /// <param name="serializerOptions">The options used to extract the schema from the specified type.</param>
-    /// <param name="inferenceOptions">The options controlling schema inference.</param>
+    /// <param name="inferenceOptions">The options controlling schema creation.</param>
     /// <returns>A <see cref="JsonElement"/> representing the schema.</returns>
     public static JsonElement CreateJsonSchema(
         Type? type,
@@ -158,7 +163,14 @@ public static JsonElement CreateJsonSchema(
         serializerOptions ??= DefaultOptions;
         inferenceOptions ??= AIJsonSchemaCreateOptions.Default;
         JsonNode schema = CreateJsonSchemaCore(type, parameterName: null, description, hasDefaultValue, defaultValue, serializerOptions, inferenceOptions);
-        return JsonSerializer.SerializeToElement(schema, JsonContext.Default.JsonNode);
+
+        // Finally, apply any schema transformations if specified.
+        if (inferenceOptions.TransformOptions is { } options)
+        {
+            schema = TransformSchema(schema, options);
+        }
+
+        return JsonSerializer.SerializeToElement(schema, JsonContextNoIndentation.Default.JsonNode);
     }
 
     /// <summary>Gets the default JSON schema to be used by types or functions.</summary>
@@ -203,25 +215,11 @@ private static JsonNode CreateJsonSchemaCore(
 
             if (hasDefaultValue)
             {
-                if (inferenceOptions.RequireAllProperties)
-                {
-                    // Default values are only used in the context of optional parameters.
-                    // Do not include a default keyword (since certain AI vendors don't support it)
-                    // and instead embed its JSON in the description as a hint to the LLM.
-                    string defaultValueJson = defaultValue is not null
-                        ? JsonSerializer.Serialize(defaultValue, serializerOptions.GetTypeInfo(defaultValue.GetType()))
-                        : "null";
-
-                    description = CreateDescriptionWithDefaultValue(description, defaultValueJson);
-                }
-                else
-                {
-                    JsonNode? defaultValueNode = defaultValue is not null
-                        ? JsonSerializer.SerializeToNode(defaultValue, serializerOptions.GetTypeInfo(defaultValue.GetType()))
-                        : null;
+                JsonNode? defaultValueNode = defaultValue is not null
+                    ? JsonSerializer.SerializeToNode(defaultValue, serializerOptions.GetTypeInfo(defaultValue.GetType()))
+                    : null;
 
-                    (schemaObj ??= [])[DefaultPropertyName] = defaultValueNode;
-                }
+                (schemaObj ??= [])[DefaultPropertyName] = defaultValueNode;
             }
 
             if (description is not null)
@@ -271,41 +269,11 @@ JsonNode TransformSchemaNode(JsonSchemaExporterContext schemaExporterContext, Js
                 }
 
                 // Include the type keyword in enum types
-                if (inferenceOptions.IncludeTypeInEnumSchemas && ctx.TypeInfo.Type.IsEnum && objSchema.ContainsKey(EnumPropertyName) && !objSchema.ContainsKey(TypePropertyName))
+                if (ctx.TypeInfo.Type.IsEnum && objSchema.ContainsKey(EnumPropertyName) && !objSchema.ContainsKey(TypePropertyName))
                 {
                     objSchema.InsertAtStart(TypePropertyName, "string");
                 }
 
-                // Disallow additional properties in object schemas
-                if (inferenceOptions.DisallowAdditionalProperties &&
-                    objSchema.ContainsKey(PropertiesPropertyName) &&
-                    !objSchema.ContainsKey(AdditionalPropertiesPropertyName))
-                {
-                    objSchema.Add(AdditionalPropertiesPropertyName, (JsonNode)false);
-                }
-
-                // Mark all properties as required
-                if (inferenceOptions.RequireAllProperties &&
-                    objSchema.TryGetPropertyValue(PropertiesPropertyName, out JsonNode? properties) &&
-                    properties is JsonObject propertiesObj)
-                {
-                    _ = objSchema.TryGetPropertyValue(RequiredPropertyName, out JsonNode? required);
-                    if (required is not JsonArray { } requiredArray || requiredArray.Count != propertiesObj.Count)
-                    {
-                        requiredArray = [.. propertiesObj.Select(prop => (JsonNode)prop.Key)];
-                        objSchema[RequiredPropertyName] = requiredArray;
-                    }
-                }
-
-                // Strip default keywords and embed in description where required
-                if (inferenceOptions.RequireAllProperties &&
-                    objSchema.TryGetPropertyValue(DefaultPropertyName, out JsonNode? defaultValue))
-                {
-                    _ = objSchema.Remove(DefaultPropertyName);
-                    string defaultValueJson = defaultValue?.ToJsonString() ?? "null";
-                    localDescription = CreateDescriptionWithDefaultValue(localDescription, defaultValueJson);
-                }
-
                 // Filter potentially disallowed keywords.
                 foreach (string keyword in _schemaKeywordsDisallowedByAIVendors)
                 {
@@ -328,20 +296,8 @@ JsonNode TransformSchemaNode(JsonSchemaExporterContext schemaExporterContext, Js
 
             if (ctx.Path.IsEmpty && hasDefaultValue)
             {
-                // Add root-level default value metadata
-                if (inferenceOptions.RequireAllProperties)
-                {
-                    // Default values are only used in the context of optional parameters.
-                    // Do not include a default keyword (since certain AI vendors don't support it)
-                    // and instead embed its JSON in the description as a hint to the LLM.
-                    string defaultValueJson = JsonSerializer.Serialize(defaultValue, ctx.TypeInfo);
-                    localDescription = CreateDescriptionWithDefaultValue(localDescription, defaultValueJson);
-                }
-                else
-                {
-                    JsonNode? defaultValueNode = JsonSerializer.SerializeToNode(defaultValue, ctx.TypeInfo);
-                    ConvertSchemaToObject(ref schema)[DefaultPropertyName] = defaultValueNode;
-                }
+                JsonNode? defaultValueNode = JsonSerializer.SerializeToNode(defaultValue, ctx.TypeInfo);
+                ConvertSchemaToObject(ref schema)[DefaultPropertyName] = defaultValueNode;
             }
 
             if (localDescription is not null)
@@ -423,7 +379,7 @@ private static void InsertAtStart(this JsonObject jsonObject, string key, JsonNo
         jsonObject.Insert(0, key, value);
 #else
         jsonObject.Remove(key);
-        var copiedEntries = jsonObject.ToArray();
+        var copiedEntries = System.Linq.Enumerable.ToArray(jsonObject);
         jsonObject.Clear();
 
         jsonObject.Add(key, value);
@@ -434,13 +390,6 @@ private static void InsertAtStart(this JsonObject jsonObject, string key, JsonNo
 #endif
     }
 
-    private static string CreateDescriptionWithDefaultValue(string? existingDescription, string defaultValueJson)
-    {
-        return existingDescription is null
-            ? $"Default value: {defaultValueJson}"
-            : $"{existingDescription} (Default value: {defaultValueJson})";
-    }
-
     private static JsonElement ParseJsonElement(ReadOnlySpan<byte> utf8Json)
     {
         Utf8JsonReader reader = new(utf8Json);

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

@@ -30,9 +30,14 @@ public static JsonElement TransformSchema(JsonElement schema, AIJsonSchemaTransf
         }
 
         JsonNode? nodeSchema = JsonSerializer.SerializeToNode(schema, JsonContext.Default.JsonElement);
+        JsonNode transformedSchema = TransformSchema(nodeSchema, transformOptions);
+        return JsonSerializer.SerializeToElement(transformedSchema, JsonContextNoIndentation.Default.JsonNode);
+    }
+
+    private static JsonNode TransformSchema(JsonNode? schema, AIJsonSchemaTransformOptions transformOptions)
+    {
         List<string>? path = transformOptions.TransformSchemaNode is not null ? [] : null;
-        JsonNode transformedSchema = TransformSchemaCore(nodeSchema, transformOptions, path);
-        return JsonSerializer.Deserialize(transformedSchema, JsonContext.Default.JsonElement);
+        return TransformSchemaCore(schema, transformOptions, path);
     }
 
     private static JsonNode TransformSchemaCore(JsonNode? schema, AIJsonSchemaTransformOptions transformOptions, List<string>? path)
@@ -169,6 +174,18 @@ private static JsonNode TransformSchemaCore(JsonNode? schema, AIJsonSchemaTransf
                     }
                 }
 
+                if (transformOptions.MoveDefaultKeywordToDescription &&
+                    schemaObj.TryGetPropertyValue(DefaultPropertyName, out JsonNode? defaultSchema))
+                {
+                    string? description = schemaObj.TryGetPropertyValue(DescriptionPropertyName, out JsonNode? descriptionSchema) ? descriptionSchema?.GetValue<string>() : null;
+                    string defaultValueJson = JsonSerializer.Serialize(defaultSchema, JsonContextNoIndentation.Default.JsonNode!);
+                    description = description is null
+                        ? $"Default value: {defaultValueJson}"
+                        : $"{description} (Default value: {defaultValueJson})";
+                    schemaObj[DescriptionPropertyName] = description;
+                    _ = schemaObj.Remove(DefaultPropertyName);
+                }
+
                 break;
 
             default:

src/Libraries/Microsoft.Extensions.AI.AzureAIInference/AzureAIInferenceChatClient.cs

@@ -29,7 +29,8 @@ internal sealed class AzureAIInferenceChatClient : IChatClient
     {
         RequireAllProperties = true,
         DisallowAdditionalProperties = true,
-        ConvertBooleanSchemas = true
+        ConvertBooleanSchemas = true,
+        MoveDefaultKeywordToDescription = true,
     });
 
     /// <summary>Metadata about the client.</summary>

src/Libraries/Microsoft.Extensions.AI.OpenAI/OpenAIChatClient.cs

@@ -30,7 +30,8 @@ internal sealed partial class OpenAIChatClient : IChatClient
     {
         RequireAllProperties = true,
         DisallowAdditionalProperties = true,
-        ConvertBooleanSchemas = true
+        ConvertBooleanSchemas = true,
+        MoveDefaultKeywordToDescription = true,
     });
 
     /// <summary>Gets the default OpenAI endpoint.</summary>

src/Libraries/Microsoft.Extensions.AI/ChatCompletion/ChatClientStructuredOutputExtensions.cs

@@ -26,9 +26,12 @@ public static partial class ChatClientStructuredOutputExtensions
     private static readonly AIJsonSchemaCreateOptions _inferenceOptions = new()
     {
         IncludeSchemaKeyword = true,
-        DisallowAdditionalProperties = true,
-        IncludeTypeInEnumSchemas = true,
-        RequireAllProperties = true,
+        TransformOptions = new AIJsonSchemaTransformOptions
+        {
+            DisallowAdditionalProperties = true,
+            RequireAllProperties = true,
+            MoveDefaultKeywordToDescription = true,
+        },
     };
 
     /// <summary>Sends chat messages, requesting a response matching the type <typeparamref name="T"/>.</summary>