HTTP Status-5xx errors. Check out the Tutorial: Route Data topic for an example with HTTP Status-200 messages.
Other Topics
High Error Rate
Example threshold alert configuration that triggers when a high number of HTTP 5xx errors per application is detected in metric events.
This is an example of an alert that is triggered when a high rate of errors is detected. This example assumes there is a Filter Processor or Route Processor that allows only Metric events, specifically