Prefer config files over package.json.
Use JSON or YAML file extensions where supported.
Prefer JSON over YAML.
Prefer .yaml over .yml.
IDEs often support schema validation of config files.
Individual config files improve discoverability and avoids cluttering package.json.
Providing a file extension allows config files to be formatted without having to whitelist and map files to a parser.
JSON should be preferred over YAML unless comments are required. JSON is more prescriptive and provides less room for error.
.yaml is the official extension recommended by YAML.
.yml is an 8.3 filename.