You can now shorten links directly from WordPress using shortcode. If you don't want to upload a plugin, you can use this method. 

It is very easy to set up, and it works with all versions of WordPress and with any theme. All links that you will shorten will be safely stored in your account.

Note: WordPress Shortcode Function is only available for those who have access to Developer API.

How to get Shortcode Function?

1. Navigate to Tools & Integration, then WordPress Integration.
2. Copy your unique PHP code from your account.
3. Go to your WordPress Admin dashboard, Appearance, and Theme File Editor.
4. On the right side, under theme files, find and click on Theme Functions (functions.php).
5. Paste the code below at the very end of the file and save it.

⚠️Warning: Do not share this plugin with anyone you do not trust, as they will have access to the full API and essentially your account.