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RFC 5545 RECURRENCE FORENSICS

ICS Calendar Recurrence & DST Validator

Audit an iCalendar file for recurrence, timezone and daylight-saving defects, then inspect the first bounded occurrences before testing importers.

Reviewed 2026-07-10

Productivity
ical.js 2.2.1Embedded VTIMEZONE only100 occurrence capSHA-256 artifacts

WHAT THIS TOOL DOES

ICS validator inputs, outputs and verification

Use it whenChecking RRULE, VTIMEZONE, EXDATE, recurrence exceptions or DST wall-time behavior.
You getA PASS, REVIEW or BLOCK ledger plus bounded source, UTC and preview-zone occurrences.
Verify withCSV evidence, timeline SVG, importer plan and a SHA-256-backed JSON receipt.

INTERPRETATION

Validate the calendar, then validate the importers.

The validator uses embedded VTIMEZONE rules for source recurrence math and the browser's Intl timezone data only for the selected preview column. It never inserts a timezone definition that was absent from the input. The Markdown export turns the evidence into a practical importer test plan.

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Event CountdownTurn a verified calendar instant into a live countdown for launch or operations checks. Scenario Tree Risk SimulatorModel the downstream risk when calendar imports, reminders or timezone behavior fail. Sun Shadow Site PlannerExplore another timezone-aware planning workflow with visible hourly evidence and exports.
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