ical2rem

Convert iCalendar (.ics) files into Remind format.

Designed to work on real-world calendar data (Google Calendar, SOGo, Outlook/Teams exports). Full RFC 5545 coverage is intentionally out of scope — see Limitations.

Features

Event types supported

iCalendar pattern	Remind output
All-day single	REM YYYY-MM-DD MSG …
All-day multi-day	REM date THROUGH date MSG …
Timed event (UTC, local, TZID)	REM date AT HH:MM DURATION HH:MM MSG …
Yearly recurrence (FREQ=YEARLY)	REM MMM DD MSG …
Weekly recurrence (FREQ=WEEKLY)	REM Mon Wed YYYY-MM-DD *7 UNTIL … MSG …
Daily recurrence (FREQ=DAILY)	REM date *N UNTIL … MSG …
Monthly by day-of-month (BYMONTHDAY)	REM N FROM … UNTIL … MSG …
Monthly by nth weekday (BYDAY=nWD)	REM Wd N FROM … UNTIL … MSG …
Exceptions (EXDATE)	PUSH-OMIT-CONTEXT + OMIT + SKIP + POP-OMIT-CONTEXT
Overrides (RECURRENCE-ID)	OMIT on original slot + single REM with new date/time
Cancellations (STATUS:CANCELLED)	OMIT only, no REM
Duration via DURATION instead of DTEND	Handled transparently
Alarms (VALARM ACTION:DISPLAY/AUDIO)	AT … +n / ++n / SCHED / WARN
Conference URL (Google Meet, Teams)	INFO "Url: …"
Windows timezone names (Outlook)	Resolved to IANA via CLDR table

Metadata lines

Each reminder can include optional INFO lines (all suppressible via flags):

REM \
    INFO "UID: …" \
    INFO "Calendar: MYCAL" \
    INFO "Location: …" \
    INFO "Description: …" \
    INFO "Url: …" \
    …

Installation

From source

Requires opam and OCaml >= 5.0.

git clone https://git.donadeo.net/pdonadeo/ical2rem
cd ical2rem
opam install . --deps-only
dune build
dune install

The binary is installed as ical2rem.

Dependencies

• icalendar — iCal parser
• timedesc + timedesc-tzdb.full + timedesc-tzlocal.unix — date/time + timezone handling
• cmdliner — CLI
• ppx_deriving.show — debug printers

Usage

ical2rem [OPTION]… FILE…

Output goes to stdout and can be redirected to a .rem file.

Pass - as a filename to read from standard input. - may appear at most once, but can be freely mixed with regular files:

curl https://example.com/calendar.ics | ical2rem - > calendar.rem
ical2rem work.ics - personal.ics > all.rem

Examples

Convert a single calendar:

ical2rem personal.ics > personal.rem

Convert multiple calendars into one file:

ical2rem work.ics personal.ics > all.rem

Sort output chronologically (oldest first):

ical2rem --sort asc personal.ics > personal.rem

Run on a server in UTC, output in a specific timezone:

ical2rem --timezone Europe/Rome personal.ics > personal.rem

Strip all metadata lines from output:

ical2rem --no-uuid --no-source --no-location --no-description --no-conference-url personal.ics

Use stdin as input calendar:

curl https://example.com/calendar.ics | ical2rem - > calendar.rem

Override calendar name in INFO lines (single file only):

ical2rem --source "Work" work.ics > work.rem

Show diagnostic warnings (skipped events, unsupported rules, etc.):

ical2rem --verbose personal.ics > personal.rem

All options

Option	Description
FILE…	One or more .ics files to convert; use - for standard input (at most once)
-z, --timezone TZ	Target timezone for output (default: local)
--sort asc|desc|original	Sort order by date (default: desc); original preserves processing order (sorted by UID within each file, last file first)
--source NAME	Override calendar name (single file only)
-v, --verbose	Print diagnostic messages on stderr
--no-uuid	Omit INFO "UID: …" lines
--no-source	Omit INFO "Calendar: …" lines
--no-location	Omit INFO "Location: …" lines
--no-description	Omit INFO "Description: …" lines
--no-conference-url	Omit INFO "Url: …" lines
--version	Print version and exit
--help	Print help and exit

Output format examples

All-day single event

REM \
    INFO "UID: abc@google.com" \
    INFO "Calendar: PERSONAL" \
    2026-06-15  MSG Birthday party

Timed event with alarm

REM \
    INFO "UID: xyz@google.com" \
    INFO "Calendar: WORK" \
    2026-05-27  AT 10:00 +30 DURATION 01:00 MSG %"Team standup%" (%b %3)

Weekly recurrence with exception

PUSH-OMIT-CONTEXT
OMIT 6 Oct 2025
REM \
    INFO "UID: …" \
    INFO "Calendar: WORK" \
    Mon 2025-09-01 *7 UNTIL 2025-12-31 SKIP AT 09:00 +15 MSG %"Standup%" (%b %3)
POP-OMIT-CONTEXT

Recurring event with modified occurrence

PUSH-OMIT-CONTEXT
OMIT 3 Jun 2015
REM \
    INFO "UID: …" \
    INFO "Calendar: PERSONAL" \
    Wed 1 FROM 2015-06-03 UNTIL 2015-06-09 SKIP MSG Monthly payment
POP-OMIT-CONTEXT
REM \
    INFO "UID: …" \
    INFO "Calendar: PERSONAL" \
    2015-06-09  MSG Monthly payment

Limitations

Recurrence rules (RRULE)

• FREQ=WEEKLY INTERVAL=N (N > 1): supported (maps to *7N).
• FREQ=MONTHLY INTERVAL=N (N > 1): not supported, event skipped with warning.
• FREQ=MONTHLY BYDAY=WD without position (every Monday of the month): not supported.
• BYSETPOS: not supported.
• FREQ=YEARLY with BYMONTH/BYDAY variants: not supported, only simple yearly (same day every year).
• RDATE (additional isolated dates): not supported, warning emitted.

Alarms (VALARM)

• ACTION:EMAIL: ignored silently.
• TRIGGER;VALUE=DATE-TIME (absolute datetime trigger): ignored silently.
• Positive triggers (after the event): ignored silently.
• RELATED=END triggers: the offset is applied as if it were RELATED=START (no warning emitted).
• REPEAT/DURATION (repeating alarms) on all-day events: ignored.

Other

• ATTENDEE, CATEGORIES, visibility/status fields: ignored.
• VTIMEZONE components: ignored; TZID names are resolved directly via IANA or the built-in Windows→IANA CLDR table.