Where exactly is my to-do list stored?
In your browser's localStorage, under the key cleanor-todo-list-v1, as JSON. It is written to disk by the browser and read back when you return to the page. Nothing is sent to a server, so it is genuinely private, but it is also genuinely fragile.
My list disappeared. Can I get it back?
No. If localStorage was cleared, the data is gone and there is no copy on any server to restore from. The usual causes are clearing browsing data, a privacy or cleaner extension, a browser reinstall, or having created the list in a private window that has since closed.
Can I see the same list on my phone?
No. localStorage is scoped to one browser on one device. There is no account and no sync, which is the trade-off for there being no server holding your data. If cross-device access matters more than privacy, use a synced to-do app instead.
Will it survive a browser restart?
Yes. That is the point of localStorage rather than session storage. Close the tab, close the browser, restart the machine, and the list is still there when you come back to this page in the same browser.
Can I back the list up?
Not through the tool: there is no export button. If the list matters, select the tasks and copy them into a note. For anything you cannot afford to lose, this is a scratch list, not a system of record.
Is there a limit to how many tasks I can add?
In practice, no. Browsers allow roughly 5 to 10 MB of localStorage per origin, which is tens of thousands of tasks. If a write ever fails because of a quota error, the tool ignores it silently, so the list in front of you might not have been saved. That is another reason not to trust it with anything critical.