Source: https://cli.nylas.com/guides/generate-ics-file-cli # Generate an ICS File from the Terminal An.ics file is the universal calendar format — attach it to an email and any client will offer to add the event. You don't need a library to make one: read an event as JSON with the Nylas CLI and assemble a VCALENDAR block, which is plain text defined by RFC 5545. This guide builds a valid.ics from a real event, covers the fields that matter, and notes when you can skip the file entirely because the CLI already sends iCalendar invites. Written by [Pouya Sanooei](https://cli.nylas.com/authors/pouya-sanooei) Software Engineer Updated June 8, 2026 > **TL;DR:** Read an event as JSON with `nylas calendar events show --id EVENT_ID --json`, then wrap its fields in a `BEGIN:VCALENDAR` / `VEVENT` block — the.ics format is plain text from RFC 5545. If you only need attendees to get an invite, skip the file: `nylas calendar events create --participants` already sends a standard iCalendar invite. Make an.ics when you need a portable, attachable file. Command references used in this guide: [`nylas calendar events show`](https://cli.nylas.com/docs/commands/calendar-events-show), [`nylas calendar events list`](https://cli.nylas.com/docs/commands/calendar-events-list), and [`nylas calendar events create`](https://cli.nylas.com/docs/commands/calendar-events-create). ## What is an ICS file? An ICS file is a calendar event in iCalendar format, the text-based standard defined by [RFC 5545](https://datatracker.ietf.org/doc/html/rfc5545). It wraps one or more `VEVENT` blocks inside a `VCALENDAR` container, and every major calendar — Google, Outlook, Apple Calendar — reads it. Attach a `.ics` to an email and the recipient's client offers to add the event with one click, regardless of which calendar they use. Because it's plain text, you don't need a library to produce one — you need the event's fields and the right line format. The Nylas CLI supplies the fields: `nylas calendar events show --id EVENT_ID --json` returns the title, start, end, location, and participants. From there, generating the file is string assembly with a handful of required properties. ## How do you build an ICS file from an event? Build the file by reading the event JSON and emitting the required iCalendar properties: `UID`, `DTSTART`, `DTEND`, `SUMMARY`, and a `DTSTAMP`. Times use the UTC form `YYYYMMDDTHHMMSSZ`. A small script maps the JSON fields to those lines and writes the `.ics` — under 20 lines of shell or Python, no dependencies. Keep the UID stable per event, since clients use it to de-duplicate and to match updates to an existing entry. If you regenerate the file for the same meeting, reuse the event's ID as the UID so an import updates rather than duplicates. The example pulls one event and writes a valid single-event calendar you can attach anywhere. ```bash #!/usr/bin/env bash # Read one event as JSON and emit a valid .ics ev=$(nylas calendar events show --id event_abc123 --json) uid=$(echo "$ev" | jq -r '.id') title=$(echo "$ev" | jq -r '.title') start=$(echo "$ev" | jq -r '.when.start_time') # epoch seconds end=$(echo "$ev" | jq -r '.when.end_time') fmt() { date -u -r "$1" +%Y%m%dT%H%M%SZ; } # epoch -> UTC ICS time cat > event.ics <