changedetection

Changedetection, or change detection, is the process of identifying whether and how data, content, or state has changed over time. In information systems, it enables automated reactions such as alerts, synchronization, or cache invalidation when sources differ from their previous versions. It is used across domains including web monitoring, file systems, databases, configuration management, and user interfaces.

Common approaches involve creating a representation of the current state (a snapshot) and comparing it to a prior snapshot. Techniques include diffing textual content, computing cryptographic or checksums (hashes) on whole items or sections, and tracking structural metadata such as timestamps or version numbers. Systems may poll sources at intervals or receive notifications from event streams, webhooks, or change data capture feeds.

Applications include monitoring web pages for updates, detecting file integrity or tampering, propagating changes between databases or caches, triggering workflows, and enabling data synchronization across distributed systems.

Challenges include choosing appropriate granularity and timing to balance responsiveness and resource use, avoiding false positives from inconsequential changes, and handling large volumes of data. Privacy, security, and consistency concerns arise in some environments, particularly when monitoring sensitive content.

Changedetection is closely related to version control, diff algorithms, checksum or hash functions, and change data capture techniques. It is a foundational capability in systems that keep distributed copies in sync or that react to evolving information.