Techniques for activity information schema discovery, schema change detection, and notification. In one embodiment, for example, a computer-implemented method for activity information schema discovery and schema change detection and notification comprises: analyzing a first set of related activity messages obtained during a first sample period; determining first schema counters for uniquely named properties identified in the first set of messages based on the analyzing of the first set of activity messages; after the first sample period, inferring a first schema from the first schema counters; analyzing a second set of related activity messages obtained during a second sample period; determining second schema counters for uniquely named properties identified in the second set of messages based on the analyzing of the second set of activity messages; after the second sample period, inferring a second schema from the second schema counters; comparing the first schema and the second schema for any differences.