JNEXT
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macOS

Download jnext-*-Darwin.dmg, open it, and drag jnext to Applications.

The first time you open it, macOS refuses to launch it and shows a dialog reading Apple could not verify "jnext" is free of malware that may harm your Mac or compromise your privacy (the exact wording varies between macOS releases). That is expected, and the next section explains why. Allowing it takes one of the three routes below; you only do it once.

Why the warning appears

JNEXT is not notarised, and that is a deliberate choice. Notarisation is Apple's approval step for software distributed outside the App Store, and it requires a paid Apple Developer Program membership renewed every year, plus a signing certificate held by the project and submitted with each release. This is a hobby project, and paying for that would not make the emulator any better.

So macOS has nothing from Apple to check the download against, and tells you so. The warning reports the absence of an approval — it does not mean anything was found wrong with the app.

If you would like to satisfy yourself that the copy you downloaded is intact, open a terminal and run:

codesign --verify --deep --strict /Applications/jnext.app

It prints nothing if every file in the bundle still matches the signature applied when the app was built, which means nothing has been altered or added since. It cannot tell you who built it — no unnotarised app can — so if that is the question that matters to you, route 3 answers it properly.

Route 1 — allow it in System Settings

This is the route that works on current macOS.

  1. Double-click jnext in Applications. macOS refuses to open it; dismiss the dialog. This step is not optional — the button in step 3 only appears after a blocked attempt.
  2. Open the Apple menu, choose System Settings, select Privacy & Security in the sidebar, and scroll down to the Security section.
  3. A line now reads "jnext" was blocked to protect your Mac, with an Open Anyway button next to it. Click it and confirm with Touch ID or your login password.
  4. Open jnext again. A last dialog asks once more; choose Open Anyway.

From then on it opens by double-click like any other app.

If you remember the older Control-click → Open trick, do not go hunting for it: on macOS 15 and later the dialog above has no Open button on it at all, which is precisely why that route cannot work here. Use the steps above instead.

Route 2 — clear the quarantine flag from a terminal

xattr -dr com.apple.quarantine /Applications/jnext.app

When your browser downloads a file, macOS tags it with an extended attribute named com.apple.quarantine — the "came from the internet" marker that triggers the check on first launch. Dragging the app out of the .dmg carries that tag onto your copy. The command removes the attribute from the app and everything inside it (-d deletes an attribute, -r recurses into the bundle), after which it opens normally.

This is you deciding to trust this particular download, which is why it names one path. Do not apply it to a whole folder, and do not turn Gatekeeper off system-wide to avoid the prompt: both of these routes cover one app and leave everything else on your Mac checked exactly as before.

Route 3 — build it yourself

The quarantine flag comes from downloading, not from running, so an app you build on your own machine never has one and there is no Gatekeeper step at all. See Building from source.