Services let people access functionality in one app from another. An app that provides services advertises the operations it can perform on particular types of data. The system then intelligently exposes its services in the app menu and in contextual menus that appear when Control-clicking text, files, and other kinds of data. For example, a service for creating a Mail message is available when you have selected text.
Give each service a short, focused title that describes exactly what it does. Strive to create a unique service title. If there are two or more services with identical names, the app name is automatically displayed after each service to distinguish them. When naming a service, use title-style capitalization and avoid definite and indefinite articles. Examples of good titles are Look Up in Dictionary and Make New Sticky Note.
Avoid providing an “Open in My App” service. People can use the Open With menu item in the Finder to open a selected file in a particular app.
Assign a keyboard shortcut to a service if it’s something people will use regularly. Don’t use standard keyboard shortcuts that the system and standard menu items already define. Note that if the keyboard shortcut you choose conflicts with a keyboard shortcut used by the current app, the app’s shortcut is always used.
Use a share extension instead of a service to share user content with other apps and social services. A share extension can either display a view that lets users edit the content or switch to its corresponding app and perform a task, like an import. See Share Extensions.
Consider including Automator actions for the services your app provides. Users can use your app's actions to create workflows that integrate your app with others on the system. See Automator Actions.
For guidance, see Services Implementation Guide.