Diablo III, Hearthstone, StarCraft II and World of Warcraft game data APIs.
Battle.net API is a free Games & Comics API that requires OAuth authentication, is served over HTTPS and supports CORS, so it can be called from the browser.
Details from develop.battle.net.

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The Battle.net API is provided by Battle.net Community Developer Portal (develop.battle.net).
Yes. The Battle.net API is listed in the Games & Comics category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The Battle.net API uses OAuth authentication, so you need to register for credentials before making requests.
Yes. The Battle.net API supports CORS, so front-end JavaScript can call it directly.
Yes. The Battle.net API is served over HTTPS, so it's safe to use in production.