From df0c102d75ecd615ec6a4a479a5cd64ab3ace252 Mon Sep 17 00:00:00 2001
From: DragonFSKY <38503900+DragonFSKY@users.noreply.github.com>
Date: Fri, 5 Jun 2026 16:54:07 -0700
Subject: [PATCH] Require Tool inputSchema during deserialization (#1600)

---
 src/ModelContextProtocol.Core/Protocol/Tool.cs         | 1 +
 tests/ModelContextProtocol.Tests/Protocol/ToolTests.cs | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/src/ModelContextProtocol.Core/Protocol/Tool.cs b/src/ModelContextProtocol.Core/Protocol/Tool.cs
index 8abbfd8..ce17d9f 100644
--- a/src/ModelContextProtocol.Core/Protocol/Tool.cs
+++ b/src/ModelContextProtocol.Core/Protocol/Tool.cs
@@ -64,6 +64,7 @@ public sealed class Tool : IBaseMetadata
     /// </para>
     /// </remarks>
     [JsonPropertyName("inputSchema")]
+    [JsonRequired]
     public JsonElement InputSchema
     {
         get => field;
diff --git a/tests/ModelContextProtocol.Tests/Protocol/ToolTests.cs b/tests/ModelContextProtocol.Tests/Protocol/ToolTests.cs
index 5b21605..d8335c0 100644
--- a/tests/ModelContextProtocol.Tests/Protocol/ToolTests.cs
+++ b/tests/ModelContextProtocol.Tests/Protocol/ToolTests.cs
@@ -105,6 +105,14 @@ public static class ToolTests
         Assert.Equal("object", typeElement.GetString());
     }
 
+    [Fact]
+    public static void ToolInputSchema_DeserializationRejectsMissingInputSchema()
+    {
+        const string json = """{"name":"test"}""";
+
+        Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<Tool>(json, McpJsonUtilities.DefaultOptions));
+    }
+
     [Theory]
     [InlineData("null")]
     [InlineData("false")]