Tutorial: How manyCalendars Stores Data (Local Storage Explained)
Posted: August 5, 2026 · 3 min read
Where your data lives
manyCalendars stores all data in two places, both entirely on your machine:
chrome.storage.local is the primary storage mechanism. This is a key-value store provided by Chrome's extension APIs. It is sandboxed to the manyCalendars extension, meaning no other extension, website, or application can access it. The data is written to your local disk as part of Chrome's internal storage directory.
Browser localStorage is used for the manyCalendars calendar view page (the tab that renders your unified calendar). This stores UI preferences like your selected view mode, color theme, and sidebar state. It follows standard browser localStorage rules and is scoped to the extension's origin.
Both storage locations are local to your browser profile. If you use multiple Chrome profiles, each profile has its own isolated copy of manyCalendars data.
What is stored
Calendar configurations. The list of calendars you have added, including their display names, colors, source type (tab sync or ICS feed), and ICS feed URLs if applicable. These configurations tell manyCalendars where to look for events.
Cached events. A local cache of calendar events that manyCalendars has read from your open tabs or ICS feeds. This cache allows the unified view to render quickly without syncing again every time you open it. Cached events include titles, times, locations, and attendee information, exactly what you see on the original calendar.
Settings and preferences. Your chosen view (day, week, month), Privacy Mode configuration, conflict detection preferences, notification settings, and any UI customizations.
License key. If you have a paid license, the key itself is stored locally to validate your plan.
What is NOT stored
This is the important part.
No passwords or credentials. manyCalendars never asks for your Google, Microsoft, or any other account credentials. It reads calendars from tabs you already have open and authenticated in your browser. Your login sessions belong to your browser, not to manyCalendars.
No OAuth tokens. There is no OAuth flow. manyCalendars does not request API access to your Google Calendar or Outlook account. It reads the rendered page content from your open tabs, the same content you see with your own eyes.
No server-side data. There is no manyCalendars server storing your information. No user database, no event database, no analytics pipeline processing your calendar data. The extension does not phone home with your schedule.
No telemetry about your calendars. manyCalendars does not track which calendars you add, how many events you have, who your meetings are with, or any other calendar-specific metadata. Basic usage analytics (extension installed, extension opened) use privacy-respecting methods with no calendar data attached.
How to clear your data
Option 1: Clear from Chrome settings. Go to chrome://extensions, find manyCalendars, click "Details," then scroll to "Clear data." This removes all chrome.storage.local data for the extension while keeping the extension installed. You will need to re-add your calendars after clearing.
Option 2: Uninstall the extension. Right-click the manyCalendars icon in your toolbar and select "Remove from Chrome." Chrome automatically deletes all extension storage data on uninstall. There is nothing left behind. No account to delete, no data retention request to file.
Option 3: Delete your Chrome profile. If you want to be thorough, deleting the Chrome profile that had manyCalendars installed removes everything, including localStorage, chrome.storage.local, and any cached page data.
What happens on uninstall
Everything disappears. Chrome's extension lifecycle guarantees that all data in chrome.storage.local is deleted when an extension is removed. The localStorage for the extension's pages is also cleared. There are no orphaned files, no leftover database entries, no ghost data on a server somewhere.
This is the privacy guarantee that only local-first architecture can make. There is no "please delete my account" email to send. No 30-day retention window. No hoping that the company actually purges your data from their backups. Uninstall and it is gone. Immediately. Completely.
That simplicity is by design. Your calendar data is sensitive, and the cleanest way to handle sensitive data is to make sure it only exists in one place, one you control. Install manyCalendars and see what privacy-by-architecture actually looks like.