In this paper we present a novel approach that allows humans to create meaningful web annotations in controlled natural language. The controlled natural language serves as a high-level interface language which enables human annotators to summarize individual web pages of a website and to express domain-specific ontological knowledge about that website in an unambiguous subset of English. The annotation process is backed up by an intelligent text editor which supports the writing process of the controlled natural language with the help of predictive interface techniques. The text editor runs as a Java applet and is connected over the Internet to a controlled natural language processor and to a reasoning service (consisting of a theorem prover and a model builder). The controlled language processor translates the summaries of web pages and the ontological knowledge about a website into first-order predicate logic and the reasoning service combines this information into a set of micro-theories for consistency and informativity checking as well as for questionanswering. Specification texts written in controlled natural language are both human-readable and machineprocessable and can be easily exported and distributed as web feeds.