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Check ICS or iCalendar Import Errors Before Upload

Check ICS structure, UID fields, and date-time formats before calendar import.

Check ICS

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How to use it

Perform a basic structural check of pasted ICS/iCalendar text. The checker counts VEVENT blocks and looks for a small set of required-looking markers.

Paste ICS text or select Sample to load a minimal example.
Select Check.
Review the event count and any structural issues found.

Calendar wrapper: Checks BEGIN:VCALENDAR and END:VCALENDAR
Event pairing: Compares BEGIN:VEVENT count with END:VEVENT count
Per-event checks: UID, DTSTART and DTSTAMP
Scope: Basic structure only; not full RFC 5545 validation

An event without DTSTART is reported directly

If a VEVENT contains UID and DTSTAMP but no DTSTART line, the result includes Event 1: DTSTART is missing..

“No basic structural issues found” does not mean the ICS is fully standards-compliant. RRULE syntax, timezone definitions, line folding and many other iCalendar rules are outside this checker.

The calendar opening and closing markers are checked first

Missing BEGIN:VCALENDAR or END:VCALENDAR is reported as a top-level structural issue.

VEVENT opening and closing counts must match

The checker compares the number of BEGIN:VEVENT and END:VEVENT markers to catch obvious truncated or unbalanced event blocks.

Only three event properties are required by this tool

Each detected event is checked for UID, DTSTART and DTSTAMP. Other properties may be important in a real calendar but are not validated here.

It is a preflight tool, not an interoperability guarantee

A file can pass these checks and still fail in a specific calendar application because deeper syntax and semantic rules are not parsed.

Related references: ISO 8601 · Date formats · World calendars