1. A computer implemented method for configuring a data contract definition for universal tag collection using a graphical user interface, comprising: in a configuration mode: generating, via a console server of a configuration subsystem, the graphical user interface for creating and managing the universal tags; displaying the graphical user interface at a client machine; receiving via the graphical interface: a selection of a data provider with universal tag availability, and one or more domain names; providing, via an event inspector tool of the configuration subsystem, an event inspector panel on the graphical user interface in response to receiving the selection of the one or more domain names; receiving, via the event inspector tool, data contract definitions, wherein each data contract definition specifies: events and corresponding event data to collect from a designated website accessed by a plurality of end users at corresponding end user devices, and transformation rules and taxonomy rules for interpreting the collected event data to generate end user profiles corresponding to the plurality of end users, the end user profiles including key-value pairs and categorizations; wherein receiving the data contract definition includes: receiving a selection of an event bookmarklet to store onto a bookmark bar of a designated website corresponding to the one or more domain names; receiving a URL corresponding to a first page of the designated website for event capture from end users who access such designated website; receiving a selection of the event bookmarklet on the bookmark bar; displaying the event inspector panel in response to the selection of the event bookmarklet, wherein the event inspector panel is overlaid on the first page and displays any previously captured event data for any events that were previously added for such first page; receiving, via the event inspector panel, input for configuring the data contract definition including adding new events for causing event data for each new event to be captured from a plurality of end users who access the first page; storing the data contract definition as a corresponding updated data contract in a database of the configuration subsystem; identifying, via a first presentation server of the configuration subsystem, the updated data contract in the database; transmitting the updated data contract from the database to the first presentation server; and generating, via the first presentation server, runtime code instructions based on the updated data contract; in a runtime mode: receiving, at a second presentation server of a runtime subsystem, the runtime code from the first presentation server to instantiate a runtime endpoint at the second presentation server; capturing, at the second presentation server during runtime, event data from the designated website, the event data specified by the data contract definition; wherein capturing event data includes providing a universal tag script, via the second presentation server, for running in the context of the designated website to instantiate a universal tag to: collect event data from the designated website, and report the collected event data to the runtime endpoint for applying the transformation and taxonomy rules; applying the transformation and taxonomy rules to the collected event data by performing an iterative loop via the runtime endpoint on the second presentation server, the iterative loop comprising: automatically determining, via a data provider servlet application, a list of runtime transformation applications corresponding to data contracts corresponding to a particular provider ID; performing, via a runtime transform application, the appropriate transformations on event-value pairs; and for each event-value pair, return a key-value pair and appropriate category identification for storage at a runtime end user profile application; categorizing the transformed event data based on the applied taxonomy rules; and storing the transformed event data in the corresponding end user profile at a profile server of the runtime subsystem; and displaying, at the client machine, a data provider configuration page corresponding to the designated website, wherein the data provider configuration page is refreshed with captured event data from the plurality of end users, the event data corresponding to previously specified events.