What does it mean when a Mac app is sandboxed?
The App Sandbox is a macOS restriction a developer opts into. A sandboxed app starts with access to almost nothing — not your files, not the network, not the camera — and has to declare each capability it wants and, for your files, be handed them by you.
What the sandbox does
It puts a boundary around the app enforced by the operating system rather than by the app's own good behaviour. Inside the boundary the app has its own container for its data. Outside it, everything is denied by default.
The practical consequence is that a sandboxed app reaches your documents when you open or drag them, or through a folder permission you grant. Even if it wanted to read your whole disk it could not, and a bug in it cannot either. That is the real value: it limits the damage from mistakes as much as from bad intent.
Every app on the Mac App Store must be sandboxed. That is the single biggest reason an app is or is not.
How we read it
From the code signature of the app bundle, where the sandbox appears as a declared entitlement. It is a direct reading of the shipped binary and not something a developer can claim on a website.
What it does not mean
An unsandboxed app is not a suspicious app, and this is the reading most likely to be taken the wrong way. Whole categories cannot function inside the sandbox: window managers, clipboard tools, launchers, backup software, disk utilities and developer tooling all need access the sandbox exists to prevent. An app sold outside the App Store has no requirement to be sandboxed, and most are not.
Nor does sandboxed mean private or safe. A sandboxed app can still have full network access and send whatever it holds wherever it likes. The sandbox limits what an app can reach on your machine, not what it does with what you give it.
A blank means we have not opened the bundle. Only a No means we looked and found no sandbox.
Questions
Is it safe to use a Mac app that is not sandboxed?
Usually, and often unavoidable. Window managers, launchers, clipboard managers, backup tools and developer software cannot do their job inside the sandbox. What matters more is whether the app is notarised and who signed it.
Does sandboxed mean the app cannot see my files?
It means it cannot reach them without you handing them over, by opening or dragging a file or granting a folder. It does not stop the app doing what it likes with a file you have opened in it.
Why are App Store apps always sandboxed?
Apple requires it for App Store distribution. An app sold from a developer's own site has no such requirement, which is why the reading splits so cleanly along how the app is sold.