If "a website" is a resource intended to be opened in a modern web browser, the answer is yes. In this case developers can safely assume the three integral part

If "a website" is a resource intended to be opened in a modern web browser, the answer is yes. In this case developers can safely assume the three integral parts - html, css, and js - are enabled and available for use. If a website - a blog - just displays some text, a raw/plain version can be provided along with it, not necessarily on the same web address. When a website displays/formats/filters some data, an API can complement it. But sometimes, a website is an app where no alternative representations would make sense. Then the answer is no. It's all about needs, requirements, possibilities, and common sense.