MCP MySQL Server

Instructions

Implementation Reference

• src/index.ts:253-283 (handler)

  The main handler function for the 'query' tool, which executes SELECT queries on the MySQL database after validation.

  private async handleQuery(args: any) {
    await this.ensureConnection();
  
    if (!args.sql) {
      throw new McpError(ErrorCode.InvalidParams, 'SQL query is required');
    }
  
    if (!args.sql.trim().toUpperCase().startsWith('SELECT')) {
      throw new McpError(
        ErrorCode.InvalidParams,
        'Only SELECT queries are allowed with query tool'
      );
    }
  
    try {
      const [rows] = await this.connection!.query(args.sql, args.params || []);
      return {
        content: [
          {
            type: 'text',
            text: JSON.stringify(rows, null, 2),
          },
        ],
      };
    } catch (error) {
      throw new McpError(
        ErrorCode.InternalError,
        `Query execution failed: ${getErrorMessage(error)}`
      );
    }
  }

• src/index.ts:125-145 (schema)

  The tool definition including name, description, and input schema for the 'query' tool in the listTools response.

  {
    name: 'query',
    description: 'Execute a SELECT query',
    inputSchema: {
      type: 'object',
      properties: {
        sql: {
          type: 'string',
          description: 'SQL SELECT query',
        },
        params: {
          type: 'array',
          items: {
            type: ['string', 'number', 'boolean', 'null'],
          },
          description: 'Query parameters (optional)',
        },
      },
      required: ['sql'],
    },
  },

• src/index.ts:197-198 (registration)

  The switch case that routes the 'query' tool call to the handleQuery function.

  case 'query':
    return await this.handleQuery(request.params.arguments);