macOS has one place to set a default app for a file type, and it is not in System Settings. The setting lives on the file itself — or rather, on the file’s type — and it is changed through Get Info. Once you know that, the rest is about which kinds of defaults you are actually trying to control.

Change the Default for a File Type

  1. Find any file of the type you want to change — a .pdf, a .png.
  2. Select it and press Command-I for Get Info.
  3. Expand Open with.
  4. Choose the app.
  5. Click Change All… and confirm.

Step 5 is the one people skip. Choosing an app without clicking “Change All” only changes that one file, which is why the setting appears not to stick.

To undo it later, repeat the process and pick the original app — there is no “reset to default” button anywhere in the interface.

Change the Default for a Protocol

Web links, mail links and tel: links are handled separately from file types, and they do live in System Settings:

  • System Settings → Desktop & Dock → Default web browser for http and https
  • Mail → Settings → General → Default email reader for mailto:

If a browser keeps stealing the default after an update, this is the setting to re-check. Some browsers ask on launch and some simply take it.

When One Default Is Not Enough

The single-default model breaks down for two groups: people who use more than one browser for different purposes, and people who work with several text editors.

Finicky applies rules to links — a URL matching a pattern opens in a specific browser. A work link goes to the work browser, everything else to the personal one, decided automatically. Choosy solves the same problem with a chooser prompt or rules, plus a browser extension for handling links from inside a page.

Our guide to privacy browsers is worth reading alongside this if the reason you want two browsers is that one of them is for sensitive sessions.

The Other Default Nobody Thinks About

Save and open dialogs remember the last folder you used, which is fine until it is the wrong folder for every app. Default Folder X adds per-app default folders and quick navigation to every save panel, so the dialog opens where the work actually lives rather than where you last were.

What Cannot Be Changed

Some associations are owned by the system and are not user-configurable: the app that handles a mounted disk image, the app that opens a .app bundle, and system-level handlers for things like x-apple.systempreferences:. If Get Info offers no alternative app for a type, that is why.

A quick way to see what is currently associated with a type:

mdls -name kMDItemContentType "somefile.pdf"

That prints the uniform type identifier, which is what the association is actually keyed on — useful when two apps both claim the same extension and you want to know which one macOS thinks owns it.

Frequently Asked Questions

Why does macOS keep reverting my default app?

An app that updates itself can re-register its file types and reclaim the association. Apps that own a document format — a note-taking app and its own bundle, for instance — do this most often. Re-applying the change after a major update is usually enough.

Can I set a default browser per website rather than for all links?

Not with macOS settings alone. That requires a rule-based link router such as Finicky or Choosy, which decides which browser to use based on the URL.