ICS Validator: Check Your Calendar File
Paste or open an .ics file. See every error against RFC 5545 with its line, the events inside, and download a repaired file. Free, no sign-up, the file stays in your browser.
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What Makes an .ics File Valid?
An .ics file is plain text in the iCalendar format (RFC 5545): one VCALENDAR with VERSION and PRODID, and inside it events with a UID, a DTSTAMP and a start. Calendars forgive a lot, but not the same things: a file that works in Google can fail in Outlook.
Required in every file
- BEGIN:VCALENDAR … END:VCALENDAR
- VERSION:2.0 and PRODID
- UID and DTSTAMP in each event
- DTSTART, then DTEND or DURATION
- Both DTEND and DURATION in one event
Common ICS Errors
What the validator flags and how to fix it.
- DTEND and DURATION together. RFC 5545 allows one. Fix: keep DTEND.
- Missing UID or DTSTAMP. Without a UID, updates create a second event. Fix: the repaired file adds both.
- TZID without VTIMEZONE. Outlook may shift the time. Fix: write times in UTC with Z, or include the VTIMEZONE.
- All-day event without VALUE=DATE. DTSTART:20261105 is not a valid date-time. Fix: DTSTART;VALUE=DATE:20261105.
- METHOD:REQUEST without ORGANIZER. Turns a download into a broken invitation. Fix: drop METHOD or use PUBLISH.
- Unfolded long lines, LF endings. Most calendars cope; strict ones don’t. Fix: the repaired file folds at 75 octets and uses CRLF.
Test in Three Calendars
A valid file is the start; a test import is the proof.
| Calendar | What to watch |
|---|---|
| Google Calendar | Imports the file; knows IANA time zone names |
| Apple Calendar | Opens the file directly from email or download |
| Outlook | Strictest about time zones and METHOD |
From Valid File to Booked Seat
Calendar files work best as part of the event journey.
- Need a New File?. The ICS calendar generator writes a valid file from a form, with UTC times.
- Event Emails From Pardot. In Account Engagement (Pardot), link the .ics file from your confirmation email or thank-you page, so registrants add the event in one click.
More Free Tools
ICS Validator FAQ
Short answers to what people ask about checking calendar files.
How do I validate an .ics file?
Paste its content or open it above. The validator checks it against RFC 5545 in your browser and lists each error with its line.
Why does my .ics file not open in Outlook?
Often a TZID without VTIMEZONE, METHOD:REQUEST without an organizer, or DTEND together with DURATION. The validator flags all three.
Which fields are required in an .ics event?
UID and DTSTAMP always, DTSTART when the file has no METHOD; around them VERSION:2.0 and PRODID in the VCALENDAR.
What does the repaired file change?
Line endings (CRLF), folding at 75 octets, a missing VERSION or PRODID, and a missing DTSTAMP or UID. Errors in your data, such as an end before the start, stay for you to fix.
Is my file uploaded?
No. It is read and checked in your browser; nothing is sent to us.
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