An API can be extended to automatically correlate events based on context. Started events for each context (e.g. threads of execution) are maintained on independent stacks. When an instrumented application starts a new transaction, the API generates a started event. A transaction correlation unit within the API can determine if the new transaction started during a previous transaction. If there is a previous started event on the stack, the new transaction started during the previous transaction. The transaction correlation unit can insert an outbound indicator into the new started event to associate the new transaction and the previous transaction. Then, the new started event can be pushed on the stack.