What is the concealed pasteboard type?
The concealed pasteboard type is a marker, written org.nspasteboard.ConcealedType, that an app adds to a copy to say the content is confidential. It is a community convention listed at nspasteboard.org, not a macOS rule.
What it means
The convention says the presence of the marker means the content should be treated as confidential. A tool that shows or stores clipboard items should obscure it, and should not save it to a file unless encrypted. Password managers set the marker when you copy a password.
Why it matters
A clipboard history keeps what you copy. Without a marker it cannot tell a password from a recipe. The marker lets it skip secrets.
How NotchStar handles it
NotchStar checks the pasteboard types for this marker and, if it is there, does not add the item to the history. The history is also held in memory only and clears when you quit. The code is in ClipboardTool.swift.
Limits
The marker works only when the app that wrote the copy sets it. An app that does not mark its copies cannot be detected. If you copy a secret from such an app, clear the history afterwards. Some password managers also use their own markers, which the convention page lists.
Related
Developers can read the underlying API at NSPasteboard. Users can start at the Clipboard feature page and why history clears on quit.
