Data source
Google embed needs no key: if you are signed in to Google in this browser with access to the calendars, private events appear. It cannot filter, merge duplicates, or do a true day view, and Google decides the final colors (closest match to yours).
Option A, public calendars: paste a Google Calendar API key. Every calendar must be set to "Make available to public" (with event details visible), otherwise it shows as "Not found".
Option B, private organization calendars (recommended for @tapi.dost.gov.ph): paste an OAuth Web Client ID and sign in. The dashboard then reads every listed calendar your Google account can already see. Sign-in only works when the page is served from an authorized origin such as http://localhost:8000, not when the file is double-clicked.
Settings, colors and names are saved in this browser only.