Google Calendar API extended properties store application-specific key-value metadata with an event. They can help match an event to an integration record without placing technical identifiers in the visible meeting description. Choose private or shared properties according to the intended metadata audience.
Choose the correct visibility
Google’s guide says private properties are specific to the calendarId and eventId used in the request. Shared properties are visible and editable by event attendees across event copies. Do not treat shared integration metadata as a secret or store credentials in it.
Update metadata narrowly
Extended properties can be set during insert, update, or patch. Google’s guidance prefers patch for changing selected properties while leaving others untouched. Reusing a key overwrites its existing value. Review the current properties before assigning names that another integration might already use.
The guide distinguishes deleting omitted properties through an update from explicitly setting a property to null in a patch. Avoid broad replacement operations when the intended change concerns one metadata field.
Verify stored values and limits
Retrieve the event through the intended calendar context and inspect the saved values. Google documents a maximum key length of forty-four characters and value length of 1,024 characters, with longer keys dropped and longer values truncated. The overall event-property limits also include private and shared properties across copies. Check these rules before relying on a long payload as a complete record. Use a controlled test and keep the authoritative business data appropriately maintained elsewhere when needed. The completed integration should preserve the intended identifier or state without exposing secrets, overwriting unrelated metadata, or treating a successful request as proof that an oversized value survived unchanged.
References
Reviewed against the linked official product guidance on November 4, 2026. Features, limits, screen labels, and access can vary by account, platform, region, and organization policy.