As long as you have Xcode installed, you can simply do:
plutil -convert json Data.plist -o Data.json
Or go one step further and create a Service with Automator:
for f in "$@"
plutil -convert json "$filename".plist -o "$filename".json
- Open Automator and create a new workflow with Service type.
- Choose Run Shell Script.
- Copy the above code snippet to the code field.
- Save the workflow. The name of the workflow is up to you, it will become the service name.
Now, just choose a .json file in Finder, pop up the context menu, choose Convert to json (or whatever name you just gave), and there should be a .plist file of the same name in the same directory.