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CalGen
A deterministic, offline iCalendar (.ics) generator and validator—built to survive real-world client incompatibilities without hiding them.
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CalGen in plain English.
CalGen is a standards-first, offline tool for generating and validating iCalendar (.ics) files that remain portable across major calendar clients. The iCalendar standard (RFC 5545) is widely implemented inconsistently, and modern clients can silently reject or structurally damage events when calendars are non-compliant—often without any visible error. CalGen addresses the portion of this problem that is structurally solvable: deterministic generation, required-field correctness, property ordering compliance, stable UID behavior, correct all-day event formatting, and timezone correctness through canonical VTIMEZONE handling. It is intentionally honest about boundaries—it generates the most defensible standard-compliant file possible and surfaces limitations explicitly rather than hiding them.
What you get.
- Timezone-safe output with canonical VTIMEZONE handling and explicit TZID strategy (no accidental floating time)
- Required-field correctness by construction (VERSION, PRODID, UID, DTSTART, DTSTAMP)
- Strict RFC 5545 property ordering—prevents modern client parsers from silently dropping fields
- Resilient recurrence generation (RRULE, EXDATE, RECURRENCE-ID) designed to reduce DST drift and exception loss
- Stable deterministic UIDs for CalGen-generated events to support reconciliation and deduplication over time
- Correct all-day event formatting (DATE semantics and exclusive end-date rules)
- SEQUENCE versioning discipline to reduce stale-event persistence when updates are imported
- Local audit logging of generation events for defensible artifacts and compliance workflows
- Deterministic outputs: same input → same output, enabling versioning and verification
Built for operators, not enterprises.
Freelancers and sole operators who track scheduled work, recurring obligations, and client deliverables in calendar format—and need those files to be reliable, portable, and provably correct. Any workflow where iCalendar output must survive Outlook, Apple Calendar, and third-party import without silent data loss.
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One-time purchase. No subscription. Lifetime access.