Calendar Extension

Add events to your calendar app while browsing.
Just select the text to be used as the event title, open the extension and you are almost done.

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Implementation to your calendar app

The url as seen in the left image can be subscribed to in most calendar-providers such as Apple Calendar or Google Calendar etc.

In Apple Calendar:

Open Calendar-app -> click on "Calendars" at the bottom -> "Add Calendar" -> "Add Subscription Calendar" -> insert your URL

In Google Calendar:

At "Other calendars", click on the "+" -> "Subscribe to calendar" -> "From URL" -> insert your URL

Others:

Other providers will not differ significantly from Apple/Google.

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Synchronisation

You can synchronise the extension between different browsers by using the same user-id in the settings. This is self-explanatory.
This may also be used to restore calendars.

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It may not be pretty but functional.