Schema validation for secure development of browser extensions

An extension schema validator may be executable within an extension process of an extension of a browser application, and may be configured to validate the extension with respect to an extension application program interface (API) that is provided in conjunction with the browser application for implementation of the extension. A browser schema validator may be executable within a browser process of the browser application, and may be configured to validate the extension with respect to the extension API. Successful validation of the extension by the extension schema validator prior to attempting validation of the extension by the browser schema validator may be required.