A system is provided for tracing end-to-end transactions. The system uses bytecode instrumentation and a dynamically injected agent to gather web server side tracing data, and a browser agent which is injected into browser content to instrument browser content and to capture tracing data about browser side activities. Requests sent during monitored browser activities are tagged with correlation data. On the web server side, this correlation information is transferred to tracing data that describes handling of the request. This tracing data is sent to an analysis server which creates tracing information which describes the server side execution of the transaction and which is tagged with the correlation data allowing the identification of the causing browser side activity. The analysis server receives the browser side information, finds matching server side transactions and merges browser side tracing information with matching server side transaction information to form tracing information that describes end-to-end transactions.