Use segment-impact after a property-level change is visible and you need to
find which pages, queries, countries, or devices moved. It compares equal-length
adjacent finalized GSC windows. The report deliberately limits conclusions to
segments retained in both windows, so its deltas are comparable without
inventing zeros for rows that disappeared from one retained result set.
Run the report
With MCP, call seo_list_reports with {"category":"diagnosis"}, then
seo_describe_report with {"id":"segment-impact"}. Then call
seo_run_report with the described report, for example
{"id":"segment-impact","params":{"site":"sc-domain:example.com","dimension":"page","days":28,"compareDays":28,"limit":20,"maxRows":50000,"unmatchedLimit":10}}.
The CLI uses the same schema:
seo reports describe segment-impact --json
seo reports run segment-impact --params '{"site":"sc-domain:example.com","dimension":"page","days":28,"compareDays":28,"limit":20,"maxRows":50000,"unmatchedLimit":10}' --json
Use either relative windows or an explicit startDate and endDate after
checking the current schema. Do not send undeclared fields.
Interpret the output
Confirm before, after, and rangeDays before reading movement. Inspect
dataStatus, source.before, source.after, and source.completeness for
provider calls, row caps, and possible truncation. selection explains invalid,
duplicate, conflicting, matched, unmatched, returned, and limited rows.
In items, clickDelta and impressionDelta are after minus before. A positive
positionDelta is worse because a larger GSC average position is lower in the
results. unmatchedSegments are observations retained in one window only; they
are not gains from or losses to zero. Read warnings, caveats, and
methodology before describing a leading segment.
Act safely
Use the top matched movers to define a smaller investigation: audit affected pages, group repeated templates, or compare query intent. Check unmatched rows separately with a wider export if they matter. Segment concentration does not establish why movement happened, and a limited or possibly truncated result cannot support an inventory-wide winner or loser claim.