feat(core): MCP Server - Capture prompt results from prompt function calls

packages/core/src/integrations/mcp-server/attributeExtraction.ts

@@ -10,6 +10,10 @@ import {
   MCP_LOGGING_LEVEL_ATTRIBUTE,
   MCP_LOGGING_LOGGER_ATTRIBUTE,
   MCP_LOGGING_MESSAGE_ATTRIBUTE,
+  MCP_PROMPT_RESULT_DESCRIPTION_ATTRIBUTE,
+  MCP_PROMPT_RESULT_MESSAGE_CONTENT_ATTRIBUTE,
+  MCP_PROMPT_RESULT_MESSAGE_COUNT_ATTRIBUTE,
+  MCP_PROMPT_RESULT_MESSAGE_ROLE_ATTRIBUTE,
   MCP_PROTOCOL_VERSION_ATTRIBUTE,
   MCP_REQUEST_ID_ATTRIBUTE,
   MCP_RESOURCE_URI_ATTRIBUTE,
@@ -377,3 +381,38 @@ export function extractToolResultAttributes(result: unknown): Record<string, str
   }
   return attributes;
 }
+
+/**
+ * Extract prompt result attributes for span instrumentation
+ * @param result - Prompt execution result
+ * @returns Attributes extracted from prompt result
+ */
+export function extractPromptResultAttributes(result: unknown): Record<string, string | number | boolean> {
+  const attributes: Record<string, string | number | boolean> = {};
+  if (typeof result !== 'object' || result === null) return attributes;
+
+  const resultObj = result as Record<string, unknown>;
+
+  if (typeof resultObj.description === 'string')
+    attributes[MCP_PROMPT_RESULT_DESCRIPTION_ATTRIBUTE] = resultObj.description;
+
+  if (Array.isArray(resultObj.messages)) {
+    attributes[MCP_PROMPT_RESULT_MESSAGE_COUNT_ATTRIBUTE] = resultObj.messages.length;
+
+    if (resultObj.messages.length > 0) {
+      const message = resultObj.messages[0];
+      if (typeof message === 'object' && message !== null) {
+        const messageObj = message as Record<string, unknown>;
+
+        if (typeof messageObj.role === 'string') attributes[MCP_PROMPT_RESULT_MESSAGE_ROLE_ATTRIBUTE] = messageObj.role;
+
+        if (typeof messageObj.content === 'object' && messageObj.content !== null) {
+          const content = messageObj.content as Record<string, unknown>;
+          if (typeof content.text === 'string') attributes[MCP_PROMPT_RESULT_MESSAGE_CONTENT_ATTRIBUTE] = content.text;
+        }
+      }
+    }
+  }
+
+  return attributes;
+}

packages/core/src/integrations/mcp-server/attributes.ts

@@ -76,6 +76,22 @@ export const MCP_TOOL_RESULT_CONTENT_COUNT_ATTRIBUTE = 'mcp.tool.result.content_
 /** Serialized content of the tool result */
 export const MCP_TOOL_RESULT_CONTENT_ATTRIBUTE = 'mcp.tool.result.content';
 
+// =============================================================================
+// PROMPT RESULT ATTRIBUTES
+// =============================================================================
+
+/** Description of the prompt result */
+export const MCP_PROMPT_RESULT_DESCRIPTION_ATTRIBUTE = 'mcp.prompt.result.description';
+
+/** Number of messages in the prompt result */
+export const MCP_PROMPT_RESULT_MESSAGE_COUNT_ATTRIBUTE = 'mcp.prompt.result.message_count';
+
+/** Role of the prompt message (for single message prompts) */
+export const MCP_PROMPT_RESULT_MESSAGE_ROLE_ATTRIBUTE = 'mcp.prompt.result.message_role';
+
+/** Content of the prompt message (for single message prompts) */
+export const MCP_PROMPT_RESULT_MESSAGE_CONTENT_ATTRIBUTE = 'mcp.prompt.result.message_content';
+
 // =============================================================================
 // REQUEST ARGUMENT ATTRIBUTES
 // =============================================================================

packages/core/src/integrations/mcp-server/correlation.ts

@@ -9,7 +9,7 @@
 import { getClient } from '../../currentScopes';
 import { SPAN_STATUS_ERROR } from '../../tracing';
 import type { Span } from '../../types-hoist/span';
-import { extractToolResultAttributes } from './attributeExtraction';
+import { extractPromptResultAttributes, extractToolResultAttributes } from './attributeExtraction';
 import { filterMcpPiiFromSpanData } from './piiFiltering';
 import type { MCPTransport, RequestId, RequestSpanMapValue } from './types';
 
@@ -69,6 +69,13 @@ export function completeSpanWithResults(transport: MCPTransport, requestId: Requ
       const toolAttributes = filterMcpPiiFromSpanData(rawToolAttributes, sendDefaultPii);
 
       span.setAttributes(toolAttributes);
+    } else if (method === 'prompts/get') {
+      const rawPromptAttributes = extractPromptResultAttributes(result);
+      const client = getClient();
+      const sendDefaultPii = Boolean(client?.getOptions().sendDefaultPii);
+      const promptAttributes = filterMcpPiiFromSpanData(rawPromptAttributes, sendDefaultPii);
+
+      span.setAttributes(promptAttributes);
     }
 
     span.end();

packages/core/src/integrations/mcp-server/piiFiltering.ts

@@ -9,6 +9,8 @@ import {
   CLIENT_ADDRESS_ATTRIBUTE,
   CLIENT_PORT_ATTRIBUTE,
   MCP_LOGGING_MESSAGE_ATTRIBUTE,
+  MCP_PROMPT_RESULT_DESCRIPTION_ATTRIBUTE,
+  MCP_PROMPT_RESULT_MESSAGE_CONTENT_ATTRIBUTE,
   MCP_REQUEST_ARGUMENT,
   MCP_RESOURCE_URI_ATTRIBUTE,
   MCP_TOOL_RESULT_CONTENT_ATTRIBUTE,
@@ -22,6 +24,8 @@ const PII_ATTRIBUTES = new Set([
   CLIENT_ADDRESS_ATTRIBUTE,
   CLIENT_PORT_ATTRIBUTE,
   MCP_LOGGING_MESSAGE_ATTRIBUTE,
+  MCP_PROMPT_RESULT_DESCRIPTION_ATTRIBUTE,
+  MCP_PROMPT_RESULT_MESSAGE_CONTENT_ATTRIBUTE,
   MCP_RESOURCE_URI_ATTRIBUTE,
   MCP_TOOL_RESULT_CONTENT_ATTRIBUTE,
 ]);

packages/core/test/lib/integrations/mcp-server/piiFiltering.test.ts

@@ -124,7 +124,7 @@ describe('MCP Server PII Filtering', () => {
         setAttributes: vi.fn(),
         setStatus: vi.fn(),
         end: vi.fn(),
-      } as any;
+      } as unknown as ReturnType<typeof tracingModule.startInactiveSpan>;
       startInactiveSpanSpy.mockReturnValueOnce(mockSpan);
 
       const toolCallRequest = {
@@ -163,6 +163,8 @@ describe('MCP Server PII Filtering', () => {
         'client.port': 54321,
         'mcp.request.argument.location': '"San Francisco"',
         'mcp.tool.result.content': 'Weather data: 18°C',
+        'mcp.prompt.result.description': 'Code review prompt for sensitive analysis',
+        'mcp.prompt.result.message_content': 'Please review this confidential code.',
         'mcp.logging.message': 'User requested weather',
         'mcp.resource.uri': 'file:///private/docs/secret.txt',
         'mcp.method.name': 'tools/call', // Non-PII should remain
@@ -180,6 +182,8 @@ describe('MCP Server PII Filtering', () => {
         'mcp.request.argument.location': '"San Francisco"',
         'mcp.request.argument.units': '"celsius"',
         'mcp.tool.result.content': 'Weather data: 18°C',
+        'mcp.prompt.result.description': 'Code review prompt for sensitive analysis',
+        'mcp.prompt.result.message_content': 'Please review this confidential code.',
         'mcp.logging.message': 'User requested weather',
         'mcp.resource.uri': 'file:///private/docs/secret.txt',
         'mcp.method.name': 'tools/call', // Non-PII should remain
@@ -193,6 +197,8 @@ describe('MCP Server PII Filtering', () => {
       expect(result).not.toHaveProperty('mcp.request.argument.location');
       expect(result).not.toHaveProperty('mcp.request.argument.units');
       expect(result).not.toHaveProperty('mcp.tool.result.content');
+      expect(result).not.toHaveProperty('mcp.prompt.result.description');
+      expect(result).not.toHaveProperty('mcp.prompt.result.message_content');
       expect(result).not.toHaveProperty('mcp.logging.message');
       expect(result).not.toHaveProperty('mcp.resource.uri');
 

packages/core/test/lib/integrations/mcp-server/semanticConventions.test.ts

@@ -434,5 +434,77 @@ describe('MCP Server Semantic Conventions', () => {
       expect(setStatusSpy).not.toHaveBeenCalled();
       expect(endSpy).toHaveBeenCalled();
     });
+
+    it('should instrument prompt call results and complete span with enriched attributes', async () => {
+      await wrappedMcpServer.connect(mockTransport);
+
+      const setAttributesSpy = vi.fn();
+      const setStatusSpy = vi.fn();
+      const endSpy = vi.fn();
+      const mockSpan = {
+        setAttributes: setAttributesSpy,
+        setStatus: setStatusSpy,
+        end: endSpy,
+      };
+      startInactiveSpanSpy.mockReturnValueOnce(
+        mockSpan as unknown as ReturnType<typeof tracingModule.startInactiveSpan>,
+      );
+
+      const promptCallRequest = {
+        jsonrpc: '2.0',
+        method: 'prompts/get',
+        id: 'req-prompt-result',
+        params: {
+          name: 'code-review',
+          arguments: { language: 'typescript', complexity: 'high' },
+        },
+      };
+
+      mockTransport.onmessage?.(promptCallRequest, {});
+
+      expect(startInactiveSpanSpy).toHaveBeenCalledWith(
+        expect.objectContaining({
+          name: 'prompts/get code-review',
+          op: 'mcp.server',
+          forceTransaction: true,
+          attributes: expect.objectContaining({
+            'mcp.method.name': 'prompts/get',
+            'mcp.prompt.name': 'code-review',
+            'mcp.request.id': 'req-prompt-result',
+          }),
+        }),
+      );
+
+      const promptResponse = {
+        jsonrpc: '2.0',
+        id: 'req-prompt-result',
+        result: {
+          description: 'Code review prompt for TypeScript with high complexity analysis',
+          messages: [
+            {
+              role: 'user',
+              content: {
+                type: 'text',
+                text: 'Please review this TypeScript code for complexity and best practices.',
+              },
+            },
+          ],
+        },
+      };
+
+      mockTransport.send?.(promptResponse);
+
+      expect(setAttributesSpy).toHaveBeenCalledWith(
+        expect.objectContaining({
+          'mcp.prompt.result.description': 'Code review prompt for TypeScript with high complexity analysis',
+          'mcp.prompt.result.message_count': 1,
+          'mcp.prompt.result.message_role': 'user',
+          'mcp.prompt.result.message_content': 'Please review this TypeScript code for complexity and best practices.',
+        }),
+      );
+
+      expect(setStatusSpy).not.toHaveBeenCalled();
+      expect(endSpy).toHaveBeenCalled();
+    });
   });
 });