Do I need an API key or any authentication?

Yes, please get your API key here: https://www.coingecko.com/en/api/pricing

For the Demo plan, please refer to this user guide for Demo plan API key.
For any paid plans, please refer to this user guide for Pro API key.

For the more demanding applications looking to scale - consider our Enterprise plans. Check it out here: https://gcko.io/enterpriseapi