Support creating and pre-filling calendar events via URL parameters

Is your feature request related to a problem? Please describe.

Nextcloud Calendar currently provides a route to create a new event, for example:

/apps/calendar/new

and it is possible to provide basic start/end information through the route.

However, there is currently no equivalent to the "Add to Google Calendar" URLs commonly used by websites and applications.

For example, Google Calendar allows external websites to open the event creation page with fields such as the title, start/end date, description and location already pre-filled.

This makes it difficult for websites supporting several calendar providers to offer a proper "Add to Nextcloud Calendar" button.

Today, the main workaround for Nextcloud users is usually to download/import an .ics file, which provides a less direct user experience.

Describe the solution you'd like

It would be useful for Nextcloud Calendar to support a URL-based event creation mechanism allowing external applications to pre-fill event information.

For example:

https://cloud.example.com/apps/calendar/new?title=My%20Event&start=2026-09-20T10:00:00Z&end=2026-09-20T11:00:00Z&location=Berlin&description=Event%20description

The Calendar app would open the normal event creation interface with these values pre-filled, while still requiring the user to review and explicitly save the event.

Ideally, the following fields could be supported:

• title
• start date/time
• end date/time
• all-day
• description
• location
• URL
• attendees, if appropriate
• recurrence information, if appropriate

The exact parameter format could of course follow Nextcloud conventions rather than the example above.

It would also be useful for the URL format to be documented and considered a stable public interface so that third-party websites and applications can safely rely on it.

This would make it possible to provide buttons such as:

Add to calendar

• Google Calendar
• Outlook
• Nextcloud Calendar (show input to fill instance url -> then open it)
• Download .ics

Describe alternatives you've considered

N/A

Additional context

This type of feature is already commonly available with other calendar providers and is frequently used for conference websites, booking platforms, event registration pages, ticketing systems and similar applications.

It could also improve interoperability around Nextcloud Calendar by giving third-party developers a simple way to integrate Nextcloud alongside Google Calendar and Outlook without requiring direct CalDAV access.

The feature should only pre-fill the event creation form and should not create an event automatically when opening the URL.

Start at the existing /apps/calendar/new route and follow how its current start and end parameters reach the event creation interface. Define the supported URL parameter format and pre-fill behavior for the requested fields, then verify that the normal review-and-save flow remains required and document the stable public URL format.