A system which enables an administrator to conveniently specify statements of a web page description which may require additional processing. The administrator may select from a list of statement types, and a language grammar corresponding to the selected statement type is displayed. The administrator may provide variable data associated with the fields of the displayed language grammar, and a rule instance is created from the language grammar and the variable data. An intermediate server may determine whether each statement of a web page description matches any of the rule instances. If a match is detected, the corresponding statement is determined to potentially require additional processing (such as modification of a URL in a reverse proxy server).