An event routing service may be used to implement lightweight reactive workflows through internal event generation and matching. The service may receive, from a client, specification of event routing rules as well as internal event rules. The internal event rules specified by the client are for matching internal events generated by the service and performing actions in response to the matching of the internal events. For example, when the event routing service determines that one of the incoming events has been successfully delivered to a target service, then the event routing service generates an internal event indicating the successful delivery. The event routing service determines that the internal event matches one of the internal event rules specified by the client. In response, the service performs an action specified by the internal event rule (e.g., send the incoming event to another target or generate a message).