Your message is encrypted in your browser and passed directly between connected browsers. The registry coordinates connections and availability; it does not receive the message or its decryption key.
The full link is the key.
Anyone with the complete link can read while a holder is reachable. Share it with care. The key stays in the link fragment, outside the network request for the page.
Open tabs keep it available.
By default, the creator's original tab must stay connected. Closing it, reloading, or going offline can end the message. The other mode lasts while at least one connected holder remains. The creator can end either mode from the original session.
Ending cannot erase a saved copy.
Ending asks cooperating tabs to clear the message. Recipients can still copy, save, photograph, or modify their client to keep it.
This does not make you anonymous.
Connection services and other browsers may see your IP address. Browser code can access the decrypted message, so privacy also depends on trusting the code delivered by this site and your device.