MySQL MCP Server

Instructions

Implementation Reference

• src/index.ts:476-526 (handler)

  The primary handler function for the 'execute_sql' tool. It validates the input arguments, ensures the query is not a SELECT statement, executes the SQL query using the MySQL connection pool, logs the activity, and returns a structured response with the result or an error message.

  private async handleExecuteSql(request: any, transactionId: string) {
    if (!isValidSqlQueryArgs(request.params.arguments)) {
      throw new McpError(
        ErrorCode.InvalidParams,
        'Invalid SQL query arguments.'
      );
    }
  
    const query = request.params.arguments.query;
  
    if (isReadOnlyQuery(query)) {
      throw new McpError(
        ErrorCode.InvalidParams,
        'SELECT queries are not allowed with execute_sql tool.'
      );
    }
  
    console.error(`[${transactionId}] Executing general SQL: ${query}`);
  
    try {
      const [result] = await this.pool.query(query);
      console.error(`[${transactionId}] SQL executed successfully`);
  
      return {
        content: [
          {
            type: 'text',
            text: JSON.stringify({
              success: true,
              message: 'SQL executed successfully',
              result
            }, null, 2),
          },
        ],
      };
    } catch (error) {
      console.error(`[${transactionId}] SQL error:`, error);
      if (error instanceof Error) {
        return {
          content: [
            {
              type: 'text',
              text: `MySQL error: ${error.message}`,
            },
          ],
          isError: true,
        };
      }
      throw error;
    }
  }

• src/index.ts:164-177 (registration)

  Registers the 'execute_sql' tool with the MCP server via setTools, defining its name, description, and input schema.

  {
    name: 'execute_sql',
    description: 'Executes any non-SELECT SQL statement (e.g., ALTER TABLE, DROP, etc.)',
    inputSchema: {
      type: 'object',
      properties: {
        query: {
          type: 'string',
          description: 'The SQL statement to execute.',
        },
      },
      required: ['query'],
    },
  },

• src/index.ts:167-176 (schema)

  Defines the input schema for the 'execute_sql' tool, specifying an object with a required 'query' string property.

  inputSchema: {
    type: 'object',
    properties: {
      query: {
        type: 'string',
        description: 'The SQL statement to execute.',
      },
    },
    required: ['query'],
  },

• src/index.ts:197-198 (registration)

  In the request handler switch statement, routes calls to the 'execute_sql' tool to its handler method.

  case 'execute_sql':
    return this.handleExecuteSql(request, transactionId);