About CalendarLint

CalendarLint is a local-first workspace for inspecting ICS calendar files before they reach a calendar application. It helps you see what is inside a file, understand interoperability risks, and make a safe copy when a repair is needed.

What Is an ICS File?

ICS, also known as iCalendar, is a standard file format for calendar data. An ICS file can contain event titles, dates, times, time zones, recurrence rules, locations, descriptions, attendees, alarms, and other calendar properties.

CalendarLint focuses on making that structure easier to inspect. It helps you reason about how a file may be interpreted by calendar applications such as Apple Calendar, Google Calendar, Microsoft Outlook, and other iCalendar-compatible clients.

What CalendarLint Does

CalendarLint lets you:

• Preview events, time zones, recurrence, and metadata.
• Diagnose malformed properties, time shifts, duplicate events, and recurrence problems.
• Compare calendar versions and review event-level changes.
• Apply safe repairs and export a separate copy for review.

The original file remains intact while you work. CalendarLint does not import events into your calendar application on your behalf.

Local Processing by Default

CalendarLint reads and analyzes ICS files in your browser. Calendar contents are not uploaded as part of the inspection, diagnosis, comparison, or repair workflow. Local projects and preferences may be stored in your browser so that you can continue working on the same device.

This local-first design makes the tool useful for investigating a file without first handing its event data to a remote service. You should still use a current browser and keep backups of important files.

Built Around iCalendar Standards

The inspection model is grounded in RFC 5545 and related iCalendar concepts, including time zones, recurrence rules, alarms, event identity, and line-level file structure. Calendar clients can still interpret extensions and unsupported properties differently, so CalendarLint presents evidence and uncertainty instead of promising identical behavior everywhere.

Learn More

The Guides explain how to open, diagnose, repair, compare, and download a safe copy of an ICS file. The Privacy Policy describes how local processing and optional analytics work.

CalendarLint is built for people who want a clearer, safer way to understand scheduling data before importing it.