On the Internet, the concept of trustworthiness has changed radically and often the brand and even the appearance of a document can mislead the reader. Some authors assert that the social reviewing mechanisms have successfully replaced any previous evaluation methodology. The thesis of this essay, on the contrary, is that today readers have to perform a complete context analysis, at least for the non institutional online resources. Instead of looking at the brand, therefore, it is essential to understand how a source has been generated. With Wikipedia, for instance, the production cycle adopted is a strong element of reliability. On the other hand, the evaluation of a single post of an individual blog needs an in-depth study. A context analysis is necessary especially when an atomic unit of information is retrieved by a search engine.