In Hack, Facebook has created a more precise language designed to catch flaws, while maintaining the rapid development cycle that has made PHP one of the most popular languages for Web development.

“This is just the first step, and we are dedicated to continuing to evolve this software to make development even easier for both our own engineers and the broader community,” wrote Verlaguet and Menghrajani. “Hack’s value is not limited to big projects: With type information, good error messages, and fast feedback, small codebases can reap the benefits of Hack as well.”

Facebook is giving a hands-on introduction to the language at a Hack Developer Day on its campus in April.