Normalize formatting
Standardize line endings, remove blank physical lines, and refold long content lines. Event meaning is left untouched.
Private by design · Free to use
Know why your calendar won’t import—before you try again.
Check an .ics file for structural, recurrence, timezone, and size problems. Then normalize its formatting or split it safely for Google Calendar.
No upload
No account
No tracking
Calendar checkRuns on your device
Step 1
Choose your ICS file
We inspect the calendar in this tab. Its contents are never sent to us.
No file selected
Up to 25 MB · nothing is uploaded
Ready for a calendar file.
Waiting for a file
Choose a calendar to begin
Your file stays in this browser.
- Canonical size
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- Events
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- Timezones
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- Issues found
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Step 2
What we found
Step 3
Prepare a safer copy
Split a large calendar
Keep recurring series and referenced timezone definitions together while creating smaller import files.
KB
Splitting becomes available after a clean check.
Ready
Your files are ready
01Local Your calendar stays on your computer.
02Conservative We do not invent missing dates or timezone rules.
03Transparent Downloads include a plain-language report.
How it works
Three useful answers from one file
ICS files are plain text, but calendars can hide tricky relationships. The doctor checks those relationships before offering a download.
Is the structure sound?
We check the calendar wrapper, required event fields, duplicated instances, malformed recurrence rules, and conflicting date properties.
Will timezones travel?
We compare timezone references with the definitions shipped in the file and flag combinations that do not make sense.
Is it too large to import?
We warn above Google Calendar’s documented 1 MB compatibility limit and can produce smaller files without breaking recurrence groups.
A worked example
A recurring meeting is more than one event
A weekly meeting can have a master rule, edited occurrences, cancellations, and its own timezone definition. Splitting those records independently can change what gets imported.
ICS Import Doctor groups them by calendar identity and refuses a split when one group cannot fit safely.
M
M
M*
One recurrence group, kept intact
Honest limits
A careful checker, not an oracle
Passing these checks does not guarantee that every calendar service will accept or display the file identically. The tool does not expand recurring events, reconstruct missing information, or rewrite event meaning.
When a structural error needs human judgment, we explain it instead of silently guessing.
Questions, answered
Before you check a calendar
Does my ICS file leave my computer?
No. The file is read by JavaScript in your browser and processed in a local browser worker. There is no upload endpoint, account, or cloud file storage.
What does “normalize” change?
Only conservative text formatting: line endings, blank physical lines, and RFC-style content-line folding. It does not change dates, event titles, attendees, recurrence rules, or timezone meaning.
Why can Google Calendar reject an ICS file?
Common causes include invalid calendar structure, missing required properties, conflicting event fields, malformed recurrence rules, timezone references, and file-size limits. Other service-specific causes may still exist.
Why is the split limit set to 900 KB?
It leaves headroom below Google Calendar’s documented 1 MB file limit. You can choose a smaller value between 100 and 950 KB.
Is ICS Import Doctor affiliated with Google?
No. This is an independent utility from ZeroesOnesAndYou. Google Calendar is a trademark of Google LLC.
Keep useful tools free
Saved you an afternoon?
ICS Import Doctor is free, private, and ad-free. If it helped, a small coffee supports maintenance and the next ZeroesOnesAndYou utility.