You can run VisualDiffer directly from macOS Finder by selecting two files or two folders.
You don't need to run VisualDiffer and then select items to compare; if you are in Finder you can do it from there.

Starting with VisualDiffer 2.1.4, Finder integration is built into the app, so you do not need to download the helper.
The helper is required only on macOS versions earlier than Ventura 13.x.
Even with the built-in integration, you must explicitly enable the Finder extension according to Apple's guidelines.

1. Open VisualDiffer and go to Settings
2. In the Finder Integration section, click "Open System Settings to enable the VisualDiffer extension"
3. Enable the VisualDiffer Finder extension in System Settings

When the extension is enabled, Finder shows the VisualDiffer service in the context menu, with actions to select items for the left and right comparison panes.

Add to the Finder context menu (under Services) a new menu item to allow file and folder comparison.

The helper is required only on macOS versions earlier than Ventura 13.x. On Ventura 13.x or later, do not install the helper.

• On Lion or above double-click the "Compare with VisualDiffer.workflow" file
• On Snow Leopard you must manually copy the file Compare with VisualDiffer.workflow inside the directory /Users/your account name/Library/Services. If the directory Services doesn't exist you must create it.

More details about installation are available here.

• In Finder, right-click the first file or folder and choose Select <name> on Left or Select <name> on Right
• Right-click the second item (it can be in another Finder window or tab), then choose Compare <name1> with <name2>
• The comparison starts automatically; if required by the Apple sandbox, you may be asked to select the files

• When elements to compare are both visible in a Finder window, simply select the two files or folders and choose "Compare with VisualDiffer" from the Services menu
• When elements to compare are in different folders
  1. Select the first element from Finder and click on the service menu item
  2. Browse to the second element and again click on the service menu item
  3. The comparison will start

If you have more Finder windows visible the first element can be selected using the menu item from one window and the second from another Finder window.