diff --git a/packages/agents-a365-tooling/src/Utility.ts b/packages/agents-a365-tooling/src/Utility.ts
index 32b0084b..f501a721 100644
--- a/packages/agents-a365-tooling/src/Utility.ts
+++ b/packages/agents-a365-tooling/src/Utility.ts
@@ -14,6 +14,8 @@ export class Utility {
   public static readonly HEADER_USER_AGENT = 'User-Agent';
   /** Header name for sending the agent identifier to MCP platform for logging/analytics. */
   public static readonly HEADER_AGENT_ID = 'x-ms-agentid';
+  /** Header name for sending the user's original message to MCP servers during tool execution. */
+  public static readonly HEADER_USER_MESSAGE = 'x-ms-usermessage';
 
   /**
    * Compose standard headers for MCP tooling requests.
@@ -52,6 +54,11 @@ export class Utility {
       headers[Utility.HEADER_SUBCHANNEL_ID] = subChannelId;
     }
 
+    const userMessage = turnContext?.activity?.text as string | undefined;
+    if (userMessage) {
+      headers[Utility.HEADER_USER_MESSAGE] = Utility.sanitizeTextForHeader(userMessage);
+    }
+
     if (options?.orchestratorName) {
       headers[Utility.HEADER_USER_AGENT] = RuntimeUtility.GetUserAgentHeader(options.orchestratorName);
     }
@@ -59,6 +66,40 @@ export class Utility {
     return headers;
   }
 
+  /**
+   * Sanitizes text for use in an HTTP header value by normalizing to ASCII-safe characters.
+   * Matches the .NET implementation in HttpContextHeadersHandler.SanitizeTextForHeader().
+   *
+   * @param input - The text to sanitize.
+   * @returns ASCII-safe text suitable for HTTP header values.
+   */
+  private static sanitizeTextForHeader(input: string): string {
+    try {
+      // Step 1: Replace non-breaking spaces with regular spaces, then trim
+      let result = input.replace(/[\u00A0\u202F]/g, ' ').trim();
+
+      // Step 2: Unicode normalize (NFD) and remove combining marks (diacritics)
+      result = result.normalize('NFD').replace(/\p{M}/gu, '');
+
+      // Step 3: Convert smart punctuation to ASCII equivalents
+      result = result
+        .replace(/[\u2018\u2019]/g, "'")   // Smart single quotes → '
+        .replace(/[\u201C\u201D]/g, '"')    // Smart double quotes → "
+        .replace(/[\u2013\u2014]/g, '-')    // En/em dashes → -
+        .replace(/\u2026/g, '...');         // Ellipsis → ...
+
+      // Step 4: Keep only printable ASCII (32-126), replace others with space
+      result = result.replace(/[^\x20-\x7E]/g, ' ');
+
+      // Step 5: Collapse whitespace and trim
+      result = result.replace(/\s+/g, ' ').trim();
+
+      return result;
+    } catch {
+      return input;
+    }
+  }
+
   /**
    * Resolves the best available agent identifier for the x-ms-agentid header.
    * Priority: TurnContext.agenticAppBlueprintId > token claims (xms_par_app_azp > appid > azp) > application name
diff --git a/tests/tooling/utility.test.ts b/tests/tooling/utility.test.ts
index 39bd416a..f952b4d9 100644
--- a/tests/tooling/utility.test.ts
+++ b/tests/tooling/utility.test.ts
@@ -240,6 +240,117 @@ describe('Utility - GetToolRequestHeaders x-ms-agentid', () => {
   });
 });
 
+describe('Utility - GetToolRequestHeaders x-ms-usermessage', () => {
+  it('should add x-ms-usermessage header when turnContext.activity.text is present', () => {
+    const mockContext = {
+      activity: {
+        text: 'What is the weather today?',
+      },
+    } as unknown as TurnContext;
+
+    const headers = Utility.GetToolRequestHeaders(undefined, mockContext);
+    expect(headers['x-ms-usermessage']).toBe('What is the weather today?');
+  });
+
+  it('should omit x-ms-usermessage header when activity.text is missing', () => {
+    const mockContext = {
+      activity: {},
+    } as unknown as TurnContext;
+
+    const headers = Utility.GetToolRequestHeaders(undefined, mockContext);
+    expect(headers['x-ms-usermessage']).toBeUndefined();
+  });
+
+  it('should omit x-ms-usermessage header when activity.text is empty string', () => {
+    const mockContext = {
+      activity: {
+        text: '',
+      },
+    } as unknown as TurnContext;
+
+    const headers = Utility.GetToolRequestHeaders(undefined, mockContext);
+    expect(headers['x-ms-usermessage']).toBeUndefined();
+  });
+
+  it('should omit x-ms-usermessage header when turnContext is undefined', () => {
+    const headers = Utility.GetToolRequestHeaders(undefined, undefined);
+    expect(headers['x-ms-usermessage']).toBeUndefined();
+  });
+
+  it('should sanitize non-breaking spaces to regular spaces', () => {
+    const mockContext = {
+      activity: {
+        text: 'hello\u00A0world\u202Ftest',
+      },
+    } as unknown as TurnContext;
+
+    const headers = Utility.GetToolRequestHeaders(undefined, mockContext);
+    expect(headers['x-ms-usermessage']).toBe('hello world test');
+  });
+
+  it('should strip diacritics from characters', () => {
+    const mockContext = {
+      activity: {
+        text: 'café résumé señor',
+      },
+    } as unknown as TurnContext;
+
+    const headers = Utility.GetToolRequestHeaders(undefined, mockContext);
+    expect(headers['x-ms-usermessage']).toBe('cafe resume senor');
+  });
+
+  it('should convert smart quotes and dashes to ASCII equivalents', () => {
+    const mockContext = {
+      activity: {
+        text: '\u201CHello\u201D \u2018world\u2019 foo\u2013bar baz\u2014qux and\u2026more',
+      },
+    } as unknown as TurnContext;
+
+    const headers = Utility.GetToolRequestHeaders(undefined, mockContext);
+    expect(headers['x-ms-usermessage']).toBe('"Hello" \'world\' foo-bar baz-qux and...more');
+  });
+
+  it('should replace non-ASCII characters with spaces', () => {
+    const mockContext = {
+      activity: {
+        text: 'hello \u4E16\u754C world',
+      },
+    } as unknown as TurnContext;
+
+    const headers = Utility.GetToolRequestHeaders(undefined, mockContext);
+    expect(headers['x-ms-usermessage']).toBe('hello world');
+  });
+
+  it('should collapse multiple whitespace into single space', () => {
+    const mockContext = {
+      activity: {
+        text: 'hello   world   test',
+      },
+    } as unknown as TurnContext;
+
+    const headers = Utility.GetToolRequestHeaders(undefined, mockContext);
+    expect(headers['x-ms-usermessage']).toBe('hello world test');
+  });
+
+  it('should coexist with all other headers', () => {
+    const mockContext = {
+      activity: {
+        channelId: 'msteams',
+        channelIdSubChannel: 'personal',
+        text: 'Find my files',
+      },
+    } as unknown as TurnContext;
+
+    const headers = Utility.GetToolRequestHeaders('my-token', mockContext, { orchestratorName: 'Claude' });
+
+    expect(headers['Authorization']).toBe('Bearer my-token');
+    expect(headers['x-ms-channel-id']).toBe('msteams');
+    expect(headers['x-ms-subchannel-id']).toBe('personal');
+    expect(headers['User-Agent']).toContain('Claude');
+    expect(headers['x-ms-usermessage']).toBe('Find my files');
+  });
+});
+
 describe('Utility - GetChatHistoryEndpoint', () => {
   const originalEnv = process.env;