CalendarLint

See what’s inside your ICS file—before you import it.

Preview every event, catch time and recurrence issues, and understand what may change in Google Calendar, Apple Calendar, or Outlook.

Check an ICS fileTry a safe example
Runs locally in your browser · No account required · Your original file stays untouched
Weekly team syncDST transition (-1h shift)
Inspection ModeEvent Conflict & DST Audit
1 Alert
Weekly team sync (Wednesday 10:00 AM EDT)

Recurring event crosses daylight saving boundary on Nov 3, 2024. European participants may see this meeting shift by one hour.

Parsed VEVENT block
RRULE:FREQ=WEEKLY;BYDAY=WE;UNTIL=20241225T150000Z
DTSTART;TZID=America/New_York:20241002T100000
EXDATE;TZID=America/New_York:20241127T100000
14 events parsed cleanly (RFC 5545)· No timezone conflicts detectedPRODID:-//CalendarLint Engine//EN

What do you need to check?

Start with the problem you can see. CalendarLint will guide you to the details only when they matter.

Read-OnlyI just want to preview an ICS file

Render full schedules safely without importing into personal feeds.

VTIMEZONEAn event shows the wrong time

Identify VTIMEZONE offsets, UTC conversions, and DST discrepancies.

VEVENTSome events are missing

Detect malformed VEVENT boundaries and silent parser drops.

RRULEA recurring event looks wrong

Debug complex RRULE statements, EXDATE exclusions, and count ceilings.

SyntaxThe file won’t import

Locate syntax errors, unescaped commas, or invalid line foldings.

Multi-ClientIt works differently in another calendar app

Compare client quirks between Google, Apple, and Outlook.

Interactive Timeline & List ViewView: Agenda · UTC-04:00
Executive Strategy Offsite09:00 AM – 11:30 AM · Hudson Yards, NY
CONFIRMED
Systems Architecture Sync01:00 PM – 02:00 PM · Every Tue until Dec 17
RRULE
Candidate Interview: Principal Security Eng03:30 PM – 04:15 PM · Google Meet link verified
PRIVATE
SHOWING 3 OF 14 PARSED VEVENT COMPONENTS Toggle Full List +

See the calendar, not a wall of text.

Open an ICS file as a clear calendar or event list. Check dates, times, locations, descriptions, and recurring events without adding anything to your personal calendar.

Calendar and list viewsRecurring events includedOriginal event detailsNo import required
Open ICS Viewer

When something looks wrong, see why.

CalendarLint connects a visible problem to the event, time, or recurrence rule behind it. Start with a plain explanation, then open the technical details if you need them.

Time Collision DetectedOVERLAP WARNING
14:00
Q3 Product Strategy Review14:00 – 15:30 (America/New_York)
Investor Update Call15:00 – 16:00 · 30m overlap
16:00
Worth reviewing

This event may appear one hour early in November.

The generator omitted standard VTIMEZONE daylight transitions, causing destination calendar apps to use unadjusted offsets.

One date in this series may not be excluded.

An EXDATE line uses a non-matching timezone identifier, which Google Calendar may silently ignore.

From file to answer, without the guesswork.

A completely local pipeline designed to provide clarity before any schedule change becomes permanent.

1

Preview

Open the file and see every event before importing it. Understand duration, participants, and status flags at a glance.

STAGE: INGESTION
2

Understand

Review clear explanations for times, recurring events, missing data, and client differences before any misinterpretation occurs.

STAGE: DIAGNOSIS
3

Fix safely

Choose the changes you understand, preview the result, and download a new sanitized file. Your original stays untouched.

STAGE: EXPORT

The same file can behave differently in each calendar app.

Check known risks for Google Calendar, Apple Calendar, Outlook Classic, and New Outlook. Each conclusion shows whether it was verified, documented, or inferred.

Calendar Behavior FactorGoogle CalendarApple CalendarOutlook ClassicNew Outlook
Floating Timezones (No TZID)Events without explicit timezone offsetVerifiedVerifiedDocumentedInferred
Recurring Exceptions (EXDATE)Skipping specific occurrences in a seriesDocumentedVerifiedVerifiedVerified
VALARM TriggersNotification lead times & soundsInferredVerifiedDocumentedDocumented
Zero Server Transmission

Private calendar details stay on your device.

CalendarLint processes ICS files in your browser. Event titles, attendees, locations, meeting links, descriptions, and original lines are not uploaded to CalendarLint.

  • No account required
  • No ads in the tool workspace
  • Optional, consent-based usage analytics
  • Original files are never overwritten
CLIENT-SIDE EXECUTION MODEL
User ICS FileLocal disk
Parser & diagnosticsSANDBOXED
In-Memory Document DOMVolatile RAM

No mystery “fix everything” button.

Some calendar problems have a safe, mechanical fix. Others depend on what you intended. CalendarLint separates the two, shows the exact change, and asks before creating a new file.

See how safe repairs work
Diff InspectorUnescaped Comma Violation
; Problematic source property:
- SUMMARY:Design Review, Q4 Planning
; RFC 5545 TEXT compliance patch:
+ SUMMARY:Design Review\, Q4 Planning

Frequently Asked Questions

Authoritative details about browser processing, file preservation, and calendar client compatibility.

Check the file before it reaches your calendar.

Preview the events, understand anything unusual, and keep your original file untouched.

Check an ICS fileExplore the guides