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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"MCP Protocol Validation Error During Initialization","articleBody":"## Summary\nThe Java MCP SQL Server successfully connects to the database and all tools are functional, but Cursor IDE shows a protocol validation error during initialization with a red error indicator. The error occurs during the MCP handshake but the server recovers and continues to work normally.\n\n## Environment\n- **OS**: Windows 10 (Build 19045)\n- **Java Version**: openjdk version \"21.0.4\" 2024-07-16 LTS\n- **MCP Server Version**: 1.0.0\n- **JAR Location**: `C:\\java-mcp-sql-server-1.0.0.jar`\n- **Database**: Oracle \n- **Cursor IDE**: 2.2.43\n\n## Configuration\n```json\n{\n  \"java-mcp-sql-server\": {\n    \"command\": \"java\",\n    \"args\": [\"-jar\", \"C:\\\\java-mcp-sql-server-1.0.0.jar\"],\n    \"env\": {\n      \"JMCP_JDBC_URL\": \"jdbc:oracle:thin:@//your-server:1521/your-database\",\n      \"JMCP_DB_USERNAME\": \"YOUR_USERNAME\",\n      \"JMCP_DB_PASSWORD\": \"YOUR_PASSWORD\",\n      \"JMCP_MODE\": \"stdio\",\n      \"JMCP_QUERY_SELECT_ONLY\": \"false\"\n    }\n  }\n}\n```\n\n## Error Details\n\n### Server Startup (Successful)\n```\n23:47:21.222 [main] INFO  com.dgdev91.mcpsql.SqlMcpServer - Starting SQL MCP Server...\n23:47:21.481 [main] INFO  com.dgdev91.mcpsql.service.DatabaseService - Oracle driver loaded successfully\n23:47:23.111 [main] INFO  com.dgdev91.mcpsql.service.DatabaseService - Successfully connected to database: ORACLE\n23:47:23.242 [main] INFO  com.dgdev91.mcpsql.SqlMcpServer - Database connection successful. Type: ORACLE, Query SELECT only: false\n```\n\n### Protocol Validation Error\nCursor IDE reports a Zod validation error during initialization:\n\n```json\n{\n  \"code\": \"invalid_union\",\n  \"unionErrors\": [\n    {\n      \"issues\": [\n        {\n          \"code\": \"invalid_union\",\n          \"unionErrors\": [\n            {\n              \"issues\": [\n                {\n                  \"code\": \"invalid_type\",\n                  \"expected\": \"string\",\n                  \"received\": \"null\",\n                  \"path\": [\"id\"],\n                  \"message\": \"Expected string, received null\"\n                }\n              ],\n              \"name\": \"ZodError\"\n            },\n            {\n              \"issues\": [\n                {\n                  \"code\": \"invalid_type\",\n                  \"expected\": \"number\",\n                  \"received\": \"null\",\n                  \"path\": [\"id\"],\n                  \"message\": \"Expected number, received null\"\n                }\n              ],\n              \"name\": \"ZodError\"\n            }\n          ],\n          \"path\": [\"id\"],\n          \"message\": \"Invalid input\"\n        },\n        {\n          \"code\": \"invalid_type\",\n          \"expected\": \"string\",\n          \"received\": \"undefined\",\n          \"path\": [\"method\"],\n          \"message\": \"Required\"\n        },\n        {\n          \"code\": \"unrecognized_keys\",\n          \"keys\": [\"error\"],\n          \"path\": [],\n          \"message\": \"Unrecognized key(s) in object: 'error'\"\n        }\n      ],\n      \"name\": \"ZodError\"\n    }\n  ],\n  \"path\": [],\n  \"message\": \"Invalid input\"\n}\n```\n\n### Recovery (Successful)\nAfter the error, the server recovers:\n```\n23:47:24.394 [info] Handling ListOfferings action, server stored: true\n23:47:24.402 [info] listOfferings: Found 5 tools\n23:47:24.402 [info] Found 5 tools, 0 prompts, and 0 resources\n```\n\n## Expected Behavior\nThe MCP server should initialize without protocol validation errors. All messages sent during initialization should conform to the MCP protocol specification.\n\n## Actual Behavior\n- Server starts successfully ✅\n- Database connection established ✅\n- Tools are available and functional ✅\n- Protocol validation error during initialization ❌\n- Red error indicator in Cursor IDE ❌\n\n## Impact\n- **Severity**: Low (cosmetic issue)\n- **Functionality**: All tools work correctly after initialization\n- **User Experience**: Red error indicator is misleading and concerning\n\n## Steps to Reproduce\n1. Configure `mcp.json` with java-mcp-sql-server\n2. Restart Cursor IDE\n3. Check MCP server logs in Cursor\n4. Observe protocol validation error during initialization\n5. Verify tools are still functional (they are)\n\n## Additional Notes\n- The error appears to be related to a message sent during initialization that contains an `\"error\"` key with a `null` id\n- The server appears to send a non-standard message format that doesn't match MCP protocol expectations\n- This might be related to error handling or logging during the initialization phase\n- All 5 tools (`list_schemas`, `list_tables`, `get_table_structure`, `query_table`, `execute_query`) work correctly after initialization\n\n\n\n---\n\n**Note**: This issue was identified while using the server with Oracle database, but it may affect other database types as well.\n\n","author":{"url":"https://github.com/ahmed98Osama","@type":"Person","name":"ahmed98Osama"},"datePublished":"2025-12-23T22:02:29.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/1/java-mcp-sql-server/issues/1"}