find_dropped_events doesn't say that buckets snap to whole intervals

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
78/100
Issue type
Documentation
Clarity
Clearly specified
Activity status
Active
Tech stack
typescript
Domain
documentation, tooling

Research direction

Start in packages/mcp-core/src/tools/catalog/find-dropped-events.ts: the interval hint text sits around lines 83-84 and 128-137, and the response mapping that omits meta.start/meta.end is at lines 212-217. Trace how the tool builds its result so a conditional note can be added when start/end fall off interval boundaries, then run the tool's tests to confirm the new hint and note appear.

Written by the indexing model from the issue text.

Description

MCP mcp-feedback-pattern

Pattern: find_dropped_events with start/end and a coarse interval returns full-interval volumes for the first and last buckets, not volumes for the requested window. Nothing in the tool output or the description says so. Callers that sum the buckets for a fixed window overcount.

Reports: 1 (Sentry MCP user feedback MCP-SERVER-GQD, python caller, server 0.42.0). The caller worked around it with interval=1h and told its user about the alignment limit.

What happens

  1. The caller passes start=<…T18:01Z>, end=<…T06:01Z>, interval=1d. The tool forwards them unchanged to GET /organizations/{org}/events-dropped/ (sampled span for this caller's call).
  2. Sentry builds the outcomes query through QueryDefinition → get_constrained_date_range (getsentry/sentry src/sentry/snuba/sessions_v2.py:451-487), which calls to_intervals (src/sentry/snuba/metrics/utils.py:414-449). That floors start to the interval and rounds end up to the next boundary. With 1d, the range becomes <day>T00:00Z to <last day + 1>T00:00Z. So the first and last buckets hold whole-day totals.
  3. The endpoint's meta.start / meta.end report the requested range, not the aligned one (src/sentry/api/endpoints/organization_events_dropped.py:233-234). The MCP tool doesn't return meta.start/meta.end at all (packages/mcp-core/src/tools/catalog/find-dropped-events.ts:212-217). Only each bucket's own start/end gives this away.
  4. The description (find-dropped-events.ts:83-84, :128-137) tells callers to "use '1d' and sum the buckets" for longer ranges, without saying that the first and last buckets can cover time outside the window.

Suggested fix (MCP side)

  • When start/end don't fall on interval boundaries, add a note that gives the aligned range that was counted and says the edge buckets are whole intervals. Suggest a finer interval (for example 1h) for exact windows.
  • Add one line to the interval hint saying buckets align to whole intervals in UTC.

Possible Sentry API follow-up (not filed): meta.start/meta.end could report the aligned range that was actually queried. Owner: whoever owns organization_events_dropped.py. The MCP note above doesn't depend on that change.

Not this issue: the same report's search_errors time-range problem is getsentry/toolkit#2146, and its explanation mismatch is getsentry/toolkit#2147.

via automation evt_905b9c478746fd9deeb853f85ad7441b · Run ID dispatch_ebd17b42670133526c625ae4ebab5254.

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