.dev is a top-level domain name operated by Google Registry. It was proposed in ICANN's new generic top-level domain (gTLD) program, and became available to the general public on March 1, 2019, with an early access period that began on February 19.
The .dev top-level domain is incorporated on the HSTS preload list, requiring HTTPS on all .dev domains without individual HSTS enlistment.
Web developers have been using .dev top-level domains within their internal networks for testing purposes for a long time. However, after Google acquired the TLD, such environments have stopped functioning on some modern web browsers.