According to yaml.org, the official file extension is .yaml
.
Quote:
Is there an official extension for YAML files?
Please use ".yaml" when possible.
However there seems to be a disagreement on the internet on which extension to use. If you look up examples on the web, many of them use the unsanctioned .yml
extension.
Searching Google returns nearly 3 times as many results for the shorter one.
49,100
15,400
So which am I supposed to use? The proper 4 letter extension suggested by the creator, or the 3 letter extension found in the wild west of the internet?
The nature and even existence of file extensions is platform-dependent (some obscure platforms don't even have them, remember) -- in other systems they're only conventional (UNIX and its ilk), while in still others they have definite semantics and in some cases specific limits on length or character content (Windows, etc.).
Since the maintainers have asked that you use ".yaml", that's as close to an "official" ruling as you can get, but the habit of 8.3 is hard to get out of (and, appallingly, still occasionally relevant in 2013).