The steady stream of new UX prototyping software continues. Last week saw the widely praised release of Principle, an OS X app that allows users to design and animate anything from multi-screen flows to individual interactions and behaviors. It’s the brainchild of Daniel Hooper, a former Apple engineer who worked on core photography apps for iOS and OS X. Hooper left the Bay Area in 2014 and moved home to Atlanta, where he was able to focus on creating Principle as a small, independent concern. I asked him a few questions about the launch over email.

Q. How did Principle start?

I left Apple a little over two years ago and spent a month or so thinking about what I wanted to do next—a prototyping tool was at the perfect intersection of my skill set, interests, and market need. I hired contractors for bits and pieces, but most of the work was done alone. Creative tools are a big project, so I’ll be growing the team now that Principle has launched.

Q. How does Principle fit into a designer’s toolbox? What does it replace, and what does it complement?

Principle is primarily a tool to help designers think about and try ideas. You never know if you’re onto something until you see it. Once you do have something you like, it’s easy to explain the idea by sharing the Principle file.

As for what it might replace or complement: that’s a tough question because designers come from many disciplines—each of which has different approaches for animation and interaction. People have described Principle as: “An easier After Effects!,” “Keynote for designers!,” “Quartz Composer without the mind-blow!” So the way Principle fits into your toolbox largely depends on your background.

Q. Is the product that shipped the product you imagined at the outset?

Definitely not. When Principle started, it was an iPad app for visual programming. I thought it would be nice for designers to design touch interfaces on a touch screen, and that complex behavior was what designers really wanted to do, if only there was an interface for it. User studies proved me wrong.

Q. What kind of user research?

I did quite a few interviews with designers in the Atlanta area. What turned out to be most helpful was to have them talk me through some of their recent work—you start to see how their tools affect what kind of work they produced. After development started, I would meet with designers every one to two weeks and silently watch them use Principle. This was painful, but it was a priceless reality check for all my designs. These user studies are the single biggest reason why Principle turned out the way it did.

Q. When you look at the market for design tools and all of the activity in it lately, all of the new indie products, what do you find notable and how do you think the market will evolve?

Technically, I expect tools will move away from web technologies—they were a convenient shortcut to get off the ground, but as more people begin prototyping and more complex things get built, the web’s limitations will start to show. If you want to see the future of software, and design, read research papers from the 1960s-70s.

I’m interested in tools that try a new approach—there have been a lot of scripting and “noodle” prototyping tools, but I think those are a poor match for the way designers think. Some argue that these tools have no limits. I disagree. They limit the way you think to that of a computer.

Q. What’s ahead for Principle?

There is a lot planned: refinements like you might expect, but a lot of totally new things too. I don’t want to ruin the surprise, but I believe that the most exciting days for Principle are ahead.