| HN Mirror

It's not. It's similar to how Imgur does it.

Imgur serves advertisements when you go to their page. But you don't get them through the API.

https://api.imgur.com/#commercial

> Your application is commercial if you're making any money with it (which includes in-app advertising), if you plan on making any money with it, or if it belongs to a commercial organization.

Calling an API and monetizing the front end it is fine. The money that Imgur loses from ads is made up in the API call monetization.

The Reddit APIs don't prohibit serving advertisements or any other form of monetization of the use of the APIs and mention it as something that your app would need to do.

https://www.redditinc.com/policies/data-api-terms

    You will disclose in your App through a privacy policy how you collect, use, store, and disclose data collected from your App Users and other visitors, including, where applicable, that third parties (e.g., advertisers) may serve content or advertisements and collect information directly from your App Users and other visitors that may include the use of cookies. In addition, by using the Data APIs, Reddit may use submitted information in accordance with our Privacy Policy.

Note that sending data to 3rd parties from a front end (e.g., advertisers) is something that is allowed provided that it is properly disclosed to the App Users or other visitors and that it may serve content or advertisements from the application.