Etsy has a public API that allows developers to query information from the Etsy website.
You can browse applications built using Etsy's API here.
If you're a developer who wants access to the Etsy API, you'll first need to sign up for an Etsy account if you don't have one already.
Once registered, you'll need a developer key. You can obtain a key at the Etsy Developer Community website. After you receive a developer key you will also be provided with a complete set of documentation to help you get started.