Amazon's Echo devices are some of the best-selling smart speakers on the market, due in no small part to the company's popular Alexa virtual assistant.

The assistant can wake you up in the morning, control your smart home or take advantage of over 25,000 skills to perform a wide variety of other tasks. The best part about Alexa's skills for many users has likely been that they're all completely free.

While that's a great deal for users, it's not so great for developers who put time and effort into creating these skills. Fortunately for them, Amazon is now giving skill developers a way to monetize their work.

On Thursday, the company announced the availability of "in-skill purchasing" (ISP) for Alexa skill developers in the US. According to the announcement, developers will now be able to make money by selling "premium digital content" within their skills.

...game products, interactive stories or even new skill features are all possible implementations of the system...

Amazon says game products, interactive stories or even new skill features are all possible implementations of ISP. The system will support both one-off purchases and subscriptions, depending on a given developer's needs.

With that said, to be clear, Amazon is not making it possible for developers to outright sell their skills - not yet, anyway.

"Skills will continue to provide a free experience for customers," Amazon's Jeff Blankenburg explained in the announcement. "This enables customers to assess the quality of the skill and understand the product for sale prior to purchasing via voice."