Definition
Each feed item should have a stable identifier. RSS typically uses guid and Atom uses id.
Item guid or atom id
Unique identifiers prevent duplicate stories and update collisions.
Checked by FeedInspector
Capability checks
Metrics
Why it matters
Clients use identifiers for deduplication and update tracking. Reused values can overwrite unrelated items or create duplicates.
How FeedInspector checks it
FeedInspector checks item.guid presence and computes guidDuplicateCount. The tech.guidUnique capability is invalid when duplicates exist.
Common problems and fixes
Problem: GUID is regenerated on every publish.
Fix: Store GUID in source records and keep it immutable.
Problem: Multiple items share one static GUID.
Fix: Use a per item key, for example database ID or canonical URL hash.
Minimal example
Stable GUID
<item>
<guid isPermaLink="false">post-2026-02-20-001</guid>
<title>New release</title>
</item>