Modify Calendar Event
modify_eventUpdate an existing Google Calendar event by changing its details such as title, time, location, description, attendees, or recurrence. Only specified fields are modified.
Instructions
Modifies an existing event in Google Calendar. TIMEZONE: Always pass the timezone parameter or include UTC offsets in start_time/end_time to avoid time offset issues. Uses PATCH semantics — only specified fields are changed, unspecified fields (including recurrence rules) are preserved.
Input Schema
TableJSON Schema
| Name | Required | Description | Default |
|---|---|---|---|
| summary | No | New event title/summary | |
| duration | No | Event duration as alternative to end_time (requires start_time). Format: a number + unit — '30s', '5m', '2h', '1.5d', '1w'. Ignored if end_time is also provided. | |
| end_time | No | New end time. Required unless 'duration' is provided alongside start_time. IMPORTANT: Always specify timezone to avoid time offset issues. Preferred: datetime with offset (e.g., '2023-10-27T11:00:00-07:00') or UTC ('2023-10-27T11:00:00Z'). Naive datetimes are localized using the timezone param or server default. Date only for all-day events (e.g., '2023-10-28'). | |
| event_id | Yes | The ID of the event to modify | |
| location | No | New event location (e.g., '123 Main St' or 'https://meet.google.com/abc-defg-hij') | |
| timezone | No | STRONGLY RECOMMENDED when using naive datetimes. IANA timezone name (e.g., 'America/New_York', 'America/Chicago'). Naive datetimes in start_time/end_time will be interpreted in this timezone. Without this, the server's DEFAULT_TIMEZONE setting is used. | |
| attendees | No | New list of attendee email addresses | |
| recurrence | No | List of RRULE, EXRULE, RDATE, or EXDATE strings for recurring events (e.g., ['RRULE:FREQ=WEEKLY;BYDAY=MO,WE,FR']). See RFC 5545. | |
| start_time | No | New start time. IMPORTANT: Always specify timezone to avoid time offset issues. Preferred: datetime with offset (e.g., '2023-10-27T10:00:00-07:00') or UTC ('2023-10-27T10:00:00Z'). Naive datetimes are localized using the timezone param or server default. Date only for all-day events (e.g., '2023-10-27'). | |
| calendar_id | No | Calendar ID where the event is located | primary |
| description | No | New event description/details | |
| user_google_email | No | The user's Google email address for Calendar access. If None, uses the current authenticated user from FastMCP context (auto-injected by middleware). |
Output Schema
TableJSON Schema
| Name | Required | Description | Default |
|---|---|---|---|
| error | No | ||
| eventId | Yes | ||
| message | Yes | ||
| success | Yes | ||
| summary | Yes | ||
| htmlLink | Yes | ||
| userEmail | Yes | ||
| calendarId | Yes | ||
| fieldsModified | Yes |