Goo.gl nicely mentions that you have a limit of 1.000.000 when using an API key.
https://developers.google.com/url-shortener/v1/getting_started
// Quotas:
By default, your registered project gets 1,000,000 requests per day for the URL Shortener API (see the Developers console for more details).
I can't find what the quota limits are when you "don't" use an API key.
The reason for this is, I could use the API key, but the server(s) will be set among various clients, and communicating in uncertain conditions where the API key could be sniffed. Aside that, OAuth would require user interaction, which wouldn't be acceptable in an automated process (which may not even haven a UI).
https://support.google.com/cloud/answer/6158857?hl=en
My expected usage would be maybe 10-20 / minute during peak hours, or max 1000 a day. Would this hit goo.gl's non API limits?