SAN FRANCISCO — When Apple began selling the Apple Watch in April, Phillip Ryu did not rush to create an app for it. Because apps on the device have limited animation and the software takes several seconds to load, Mr. Ryu, a founder of Impending, which makes mobile games, said he was constrained in terms of what programs he could create for the watch.

Now, he is rethinking that decision. On Monday, Apple will begin its annual developer conference, where the company is set to release new tools for software developers to create smarter apps that will gain deep access to the watch’s heart-rate and motion sensors, among other components.

“It feels like we have both our hands tied behind our backs, and that’s why you haven’t seen anything really impressive,” Mr. Ryu said about apps for the watch, which was released with around 3,500 programs. Now, “it sounds like they plan on untying our hands.”

Gaining more apps for Apple Watch is crucial to Timothy D. Cook, Apple’s chief executive. The device is his first new product since taking the reins of the company in 2011. Apps from outside developers helped increase sales of Apple’s iPhones and iPads by vastly expanding their capabilities. Likewise, third-party apps could become important selling points for the watch, which now is primarily an expensive timepiece that requires an iPhone to operate.