diff --git a/dotnet/src/Microsoft.Agents.AI.Hyperlight/Internal/InstructionBuilder.cs b/dotnet/src/Microsoft.Agents.AI.Hyperlight/Internal/InstructionBuilder.cs
index a4c2a43266d..e198987f8f9 100644
--- a/dotnet/src/Microsoft.Agents.AI.Hyperlight/Internal/InstructionBuilder.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Hyperlight/Internal/InstructionBuilder.cs
@@ -2,6 +2,7 @@
 
 using System.Collections.Generic;
 using System.Text;
+using System.Text.Json;
 using Microsoft.Extensions.AI;
 
 namespace Microsoft.Agents.AI.Hyperlight.Internal;
@@ -42,7 +43,9 @@ public static string BuildContextInstructions(bool toolsVisibleToModel)
     /// <remarks>
     /// Host-side filesystem paths are intentionally omitted from the
     /// description — only sandbox-visible mount paths are exposed to the
-    /// model.
+    /// model. Host-tool parameter shapes come from each tool's existing
+    /// <c>JsonSchema</c> and are documentation for the model only; they do
+    /// not change the <c>execute_code</c> input schema.
     /// </remarks>
     public static string BuildExecuteCodeDescription(
         IReadOnlyList<AIFunction> tools,
@@ -72,6 +75,18 @@ public static string BuildExecuteCodeDescription(
                 }
 
                 sb.AppendLine();
+
+                // Surface the host tool's existing parameter schema so the model can see
+                // names, requiredness, descriptions, enums, and nested shapes.
+                // JSON Schema roots are objects or booleans (true/false); reject other kinds.
+                JsonElement schema = tool.JsonSchema;
+                if (schema.ValueKind is JsonValueKind.Object or JsonValueKind.True or JsonValueKind.False)
+                {
+                    sb.AppendLine("  Parameters (JSON Schema):");
+                    sb.Append("  ");
+                    sb.Append(schema.GetRawText());
+                    sb.AppendLine();
+                }
             }
         }
 
diff --git a/dotnet/tests/Microsoft.Agents.AI.Hyperlight.UnitTests/InstructionBuilderTests.cs b/dotnet/tests/Microsoft.Agents.AI.Hyperlight.UnitTests/InstructionBuilderTests.cs
index deab2b75e9b..d02dc1e622d 100644
--- a/dotnet/tests/Microsoft.Agents.AI.Hyperlight.UnitTests/InstructionBuilderTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.Hyperlight.UnitTests/InstructionBuilderTests.cs
@@ -1,13 +1,20 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 using System.Collections.Generic;
+using System.ComponentModel;
+using System.Linq;
+using System.Text.Json;
+using System.Threading.Tasks;
 using Microsoft.Agents.AI.Hyperlight.Internal;
 using Microsoft.Extensions.AI;
+using Moq;
 
 namespace Microsoft.Agents.AI.Hyperlight.UnitTests;
 
 public sealed class InstructionBuilderTests
 {
+    private static readonly AIAgent s_mockAgent = new Mock<AIAgent>().Object;
+
     [Fact]
     public void BuildContextInstructions_HiddenTools_MentionsCallTool()
     {
@@ -69,6 +76,80 @@ public void BuildExecuteCodeDescription_WithTools_IncludesToolNames()
         Assert.Contains("fetch docs", text);
     }
 
+    [Fact]
+    public async Task BuildExecuteCodeDescription_WithParameterizedTools_IncludesHostToolJsonSchemaAsync()
+    {
+        // Arrange — zero-parameter tools already have coverage above; this locks the
+        // host-tool JsonSchema gap tracked by microsoft/agent-framework#8446.
+        // Stick to reflection-friendly primitives so AOT/source-gen test hosts can build the schema.
+        static string Lookup(
+            [Description("Search text")] string query,
+            [Description("Maximum results")] int limit = 10) => $"{query}:{limit}";
+
+        var tool = AIFunctionFactory.Create(
+            Lookup,
+            name: "lookup",
+            description: "Look up an item.");
+
+        // Act
+        var text = InstructionBuilder.BuildExecuteCodeDescription(
+            tools: [tool],
+            fileMounts: [],
+            allowedDomains: [],
+            hasHostInputDirectory: false);
+
+        // Assert — model-facing description must carry the host tool parameter schema.
+        Assert.Contains("lookup", text);
+        Assert.Contains("Look up an item.", text);
+        Assert.Contains("Parameters (JSON Schema)", text);
+        Assert.Contains(tool.JsonSchema.GetRawText(), text);
+        Assert.Contains("query", text);
+        Assert.Contains("Search text", text);
+        Assert.Contains("limit", text);
+        Assert.Contains("Maximum results", text);
+
+        // Host schemas are documentation only; they must not replace execute_code's code-only input.
+        using var executeCode = new HyperlightExecuteCodeFunction(new HyperlightCodeActProviderOptions
+        {
+            Tools = [tool],
+        });
+        Assert.Contains("\"code\"", executeCode.JsonSchema.GetRawText());
+        Assert.DoesNotContain("\"query\"", executeCode.JsonSchema.GetRawText());
+        Assert.DoesNotContain("\"limit\"", executeCode.JsonSchema.GetRawText());
+
+        using var provider = new HyperlightCodeActProvider(new HyperlightCodeActProviderOptions
+        {
+            Tools = [tool],
+        });
+        var context = await provider.InvokingAsync(
+            new AIContextProvider.InvokingContext(s_mockAgent, session: null, new AIContext()));
+        var providerFn = Assert.IsAssignableFrom<AIFunction>(context!.Tools!.First());
+        Assert.Contains("\"code\"", providerFn.JsonSchema.GetRawText());
+        Assert.DoesNotContain("\"query\"", providerFn.JsonSchema.GetRawText());
+        Assert.DoesNotContain("\"limit\"", providerFn.JsonSchema.GetRawText());
+    }
+
+    [Theory]
+    [InlineData("true")]
+    [InlineData("false")]
+    public void BuildExecuteCodeDescription_WithBooleanJsonSchema_IncludesBooleanRoot(string schemaJson)
+    {
+        // Arrange — boolean JSON Schema roots are valid and must surface to the model.
+        var tool = new BooleanSchemaTool("gate", "Always-on gate.", schemaJson);
+
+        // Act
+        var text = InstructionBuilder.BuildExecuteCodeDescription(
+            tools: [tool],
+            fileMounts: [],
+            allowedDomains: [],
+            hasHostInputDirectory: false);
+
+        // Assert
+        Assert.Contains("gate", text);
+        Assert.Contains("Parameters (JSON Schema)", text);
+        Assert.Contains(schemaJson, text);
+    }
+
     [Fact]
     public void BuildExecuteCodeDescription_WithFilesystem_IncludesSandboxPathsOnly()
     {
@@ -105,4 +186,27 @@ public void BuildExecuteCodeDescription_WithAllowedDomains_IncludesNetworkSectio
         Assert.Contains("GET", text);
         Assert.Contains("POST", text);
     }
+
+    private sealed class BooleanSchemaTool : AIFunction
+    {
+        private readonly JsonDocument _schemaDocument;
+
+        public BooleanSchemaTool(string name, string description, string schemaJson)
+        {
+            this.Name = name;
+            this.Description = description;
+            this._schemaDocument = JsonDocument.Parse(schemaJson);
+        }
+
+        public override string Name { get; }
+
+        public override string Description { get; }
+
+        public override JsonElement JsonSchema => this._schemaDocument.RootElement;
+
+        protected override ValueTask<object?> InvokeCoreAsync(
+            AIFunctionArguments arguments,
+            System.Threading.CancellationToken cancellationToken) =>
+            new((object?)null);
+    }
 }