ICS Validator

A fast online ICS validator for developers and calendar admins to verify iCalendar syntax, components, and time zone rules.

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< 15ms

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100%

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4.9 / 5.0

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About This Tool

The ICS Validator checks iCalendar files for RFC 5545 compliance and structural correctness. It analyzes the VCALENDAR block and its components (VEVENT, VTIMEZONE, VTODO) to ensure required properties exist and formats are valid. Conceptually, it parses the text representation, unfolds folded lines, and validates each line against iCalendar syntax. The tool is beneficial to developers integrating calendar data, system engineers exporting schedules, and administrators validating shared ICS files. Its unique value lies in precise, line-numbered diagnostics and strict adherence to standards, enabling reliable interoperability across clients. Core features include syntax validation, component presence checks, and timezone consistency reporting; advanced capabilities cover RRULE/RDATE validation and timezone reference verification using a local database. Use cases range from validating export workflows to debugging import failures in calendar apps. Outputs are designed to be machine-ready for automated remediation while remaining human-readable for troubleshooting. The tool does not modify the source ICS and does not perform network lookups, ensuring a deterministic validation pass.

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How to Use

Provide ICS content as input to the validator.
Trigger validation by submitting the data or letting it run automatically.
Review the reported errors and warnings with line references.
Correct issues in the source ICS if fixes are suggested.
Re-run validation until is_valid is true or no critical errors remain.

Frequently Asked Questions

Find Quick Answers

What constitutes a valid ICS file?

A valid ICS file begins with a VCALENDAR block, includes required properties (VERSION, PRODID, CALSCALE), and contains one or more event-related components like VEVENT. All BEGIN/END pairs must be properly nested and line folding must be correct.

How does time zone handling work?

Time zones are validated via TZID references and must correspond to a defined VTIMEZONE block or a valid UTC time with Z suffix. The validator checks for consistency between TZID usage and available timezone definitions.

Can the validator auto-fix issues?

No. The tool reports errors with precise locations and guidance but does not rewrite or mutate the ICS content. Users should apply fixes in the source data and re-validate.

Are there limitations to validation?

The tool focuses on structural compliance and syntax. It does not assess the semantic meaning of events, recurrence semantics beyond basic syntax, or external references such as remote resources.

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