Does WhatsApp offer an open API?

I wonder if there is an open API to access WhatsApp through an internet protocol? The concrete question is:

1. Is there a way to send a message to a list of WhatsApp users from an internet server?
2. Is there any open concept for authentication?
3. Or - is WhatsApp at the end a closed system without any open API through an internet protocol?

3. is the correct answer. WhatsApp is intentionally a closed system without an API for external access.

There were several projects available that reverse engineered the WhatsApp webservice interfaces. However, to my knowledge all of them are now discontinued/defunct due to legal action against them from WhatsApp.

For mobile phone applications there is a limited URL-Scheme-API available on IPhone and Android (Android-intent possible as well).

WhatsApp does not have a API available for public use. As you put it, it's a closed system.

However, they provide several other ways in which your iPhone application can interact with WhatsApp: through custom URL schemes, share extension and through the Document Interaction API.

>See this WhatsApp FAQ article.

1. It looks possible. This info on Github describes how to create a java program to send a message using the whatsapp encryption protocol from WhisperSystems.

2. No. See the whatsapp security white paper.

3. See #1.