Recurring Schedule Debugger
Check which dates a calendar repeat rule creates. Find skipped dates and see how time zones and clock changes affect the schedule.
How can I check a calendar repeat rule?
Paste an RRULE and set its start date and time zone. Run the check to see the dates it creates, adds or skips. Choose a date to find out why it is included or missing. Download the schedule as CSV or ICS.
Every date has a reason.
Follow a recurrence from its rule to the dates it creates.
Dates in the preview range are inclusive. Local timestamps use YYYY-MM-DDTHH:mm; time zones use IANA names such as America/Toronto.
Your explanation and report will appear here.
Three simple steps
How to use Recurring Schedule Debugger
Enter a time, recurrence rule or local calendar file.
Choose the relevant date range and inspect the explanation or overlaps.
Download the report and save a project to reopen your inputs.
Common questions
Good to know
Understand the result.
Keep the original.
Is this tool free, and are my files uploaded?
This tool is free with no account required. The work happens in your browser. Your input and files are not sent to a processing server.
What are the limits and details?
Calculations run in a cancellable browser worker. Time-zone offsets use this browser's installed database unless an imported calendar supplies its own VTIMEZONE. Save a local project file to retain your inputs; files are not uploaded and invitations are not sent.
Hourly through yearly rules; one RRULE up to 2,000 characters; 500 additions and exclusions each; a 366-day preview within 20 years of DTSTART; 20,000 candidate iterations and 5,000 result rows. UNTIL must be UTC. Calendar export supports up to 2,000 included occurrences.