Minecraft wiki entry for NBT_path_format, associated text: The valid character set (without quote) for a path seems to be all non-whitespace characters, as long as any opening brackets and braces ([ and {) are closed and at the end of each term (that is, followed by nothing but a period or the end of the path—. or ). That being said, the "reasonable character set" for defining a data tag includes all lowercase and uppercase letters, numbers, underscore, period, and square and curly brackets (Regular expression: [a-zA-Z0-9\.[\]{}]*)