Calendar conflict checker

What it does

Find overlapping events in imported ICS calendars within an inclusive date range and export a structured report.

How to use it

1. Import 1–10 ICS files, 2 MB combined, at most 2,000 event definitions. Choose up to 366 inclusive UTC dates.
2. Expansion is capped at 50,000 steps, 5,000 occurrences and 10,000 conflicts, with a cancellable 15-second worker deadline. Unsupported or over-limit input returns an error rather than a partial report.
3. Review the first 100 overlapping pairs on screen and download all conflicts as JSON. Inputs remain on your device.

Example

Events 10:00–11:00 and 10:30–11:30 conflict; an event beginning exactly at 11:00 does not overlap the first.

Methodology

ICAL.js expands recurrence rules and exclusion dates. Individual recurrence overrides replace their original occurrence. A sorted interval scan finds overlapping pairs; cancelled, transparent and zero-duration events do not block time.

Limitations

Floating times and all-day dates are interpreted as UTC. Named zones require embedded VTIMEZONE. THISANDFUTURE and RDATE periods are rejected. Identical UID/start/end occurrences across imports are deduplicated. No remote calendar sync.

Automation

This tool runs in your browser. No upload API or MCP endpoint is available.