Allowed characters in map key identifier in YAML?

Question

Which characters are and are not allowed in a key (i.e. example in example: "Value") in YAML?

Answer 1

According to the YAML 1.2 specification simply advises using printable characters with explicit control characters being excluded (see here):

In constructing key names, characters the YAML spec. uses to denote syntax or special meaning need to be avoided (e.g. '#' denotes comment, '>' denotes folding, '-' denotes list, etc.).

Essentially, you are left to the relative coding conventions (restrictions) by whatever code (parser/tool implementation) that needs to consume your YAML document. The more you stick with alphanumerics the better; it has simply been our experience that the underscore has worked with most tooling we have encountered.

It has been a shared practice with others we work with to convert the period character '.' to an underscore character '_' when mapping namespace syntax that uses periods to YAML. Some people have similarly used hyphens successfully, but we have seen it misconstrued in some implementations.

Answer 2

Any character (if properly quoted by either single quotes 'example' or double quotes "example"). Please be aware that the key does not have to be a scalar ('example'). It can be a list or a map.