1. A method comprising: acquiring, at a web browser on a client device via a network, from a provider of a website, a webpage of the web site, the webpage comprising text data including descriptive data embedded in the text data conforming to a particular format; executing, by the client device, an intermediary process when the webpage is loaded by the web browser; in response to loading the webpage and prior to display of the webpage, identifying, by the intermediary process, the descriptive data embedded in the text data by searching the text data to determine if the text data includes data matching the particular format using a method chosen from a group of methods consisting of string matching, regular expression pattern matching, and searching for metadata files of known formats; selecting, by the intermediary process, an online data source based on the particular format, the online data source being separate from the website and unrelated to the provider of the website and having additional content relevant to the webpage; transmitting, by the intermediary process, the identified descriptive data to the online data source; receiving, by the intermediary process, a response from the online data source, the response including additional content related to the identified descriptive data for inclusion in the webpage; modifying, by the intermediary process, the webpage to include at least a portion of the additional content as an overlay; and displaying, by the web browser, the webpage and the portion of the additional content on a display of the client device as the overlay of the webpage, such that the additional content is displayed in association with content of the webpage.