ICS File Validator
Check your ICS (iCalendar) files against the RFC 5545 standard. Find errors that break calendar imports and warnings that hurt compatibility — before your users do.
Drop your ICS file here or click to browse
Supports .ics files
— or paste iCalendar text —
What Gets Checked
🏗️Structure & Required Properties
VERSION and PRODID on the calendar, UID and DTSTAMP on every event — the properties RFC 5545 makes mandatory and many generators forget.
📅Date & Time Logic
End dates before start dates, DATE vs DATE-TIME mismatches, DTEND together with DURATION, and non-exclusive all-day end dates.
🌍Timezone Problems
TZID references without a matching VTIMEZONE, unknown timezone names, and empty VTIMEZONE definitions — the most common cause of events showing at the wrong time.
📏Formatting Rules
CRLF line endings, the 75-octet line folding limit, and control characters — formatting details that strict parsers reject outright.
🔁Duplicates & Recurrence
Duplicate UIDs (while correctly allowing recurrence exceptions), unparseable RRULEs, and rules that combine UNTIL with COUNT.
✉️Values & Addresses
Invalid STATUS values and ORGANIZER/ATTENDEE entries that are not proper mailto: calendar addresses.
How to Use the ICS Validator
Upload or Paste
Drop an .ics file or paste iCalendar text directly
Review Findings
Errors, warnings and info items with the exact event and rule involved
Fix and Re-check
Fix issues in our ICS Editor, then validate again until everything is green
Frequently Asked Questions
What is the difference between errors and warnings?
Errors are violations of RFC 5545 that can make calendar applications reject the file or misinterpret events. Warnings are interoperability issues — the file usually still imports, but some clients may behave unexpectedly.
My file has warnings — will it still work?
In most cases, yes. Popular clients like Google Calendar and Outlook are forgiving. Fixing warnings makes your file work reliably everywhere, including stricter parsers.
Is my calendar data uploaded anywhere?
No. Validation runs entirely in your browser — the file never leaves your device.
Can the validator fix problems automatically?
The validator only reports issues. To fix them, open the file in our ICS Editor, or regenerate it with one of our converters — they produce RFC-compliant output.