Go to *File | Settings | Tools | External Tools* for Windows and Linux or *WebStorm | Preferences | Tools | External Tools* for OS X and click **+** to add a new tool. Let’s name it **Prettier**.
> If on the other hand you have `prettier` installed locally, replace the **Program** with `./node_modules/.bin/prettier` (on OS X and Linux) or `.\node_modules\.bin\prettier.cmd` (on Windows).
Now when you setup **External Tool** I guess you want to add hotkey for it. Go to *File | Settings | Keymap* for Windows and Linux *WebStorm | Preferences | Keymap* and type external tool name in search box.
To automatically format using `prettier` on save, you can use a file watcher.
Go to *File | Settings | Tools | File Watchers* for Windows and Linux or *WebStorm | Preferences | Tools | File Watchers* for OS X and click **+** to add a new tool. Let’s name it **Prettier**.
* **Program** set the full path to a `prettier` executable, such as `/Users/developer/repo/jest/node_modules/.bin/prettier` (on OS X and Linux) or `C:/\Users\developer\repo\jest\node_modules\.bin\prettier.cmd` (on Windows).