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Strict YAML


ytt includes strict YAML subset mode that tries to remove any kind of ambiguity in user’s intent when parsing YAML.

Unlike full YAML, strict subset:

  • only supports specifying nulls as "" or null
  • only supports specifying bools as false or true
  • only support basic int and float declarations
    • prefix, suffix, octal notation, etc are not supported
  • requires strings with whitespace to be explicitly quoted
  • requires strings with colon to be explicitly quoted
  • requires strings with triple-dash (document start) to be explicitly quoted



$ echo 'key: yes' | ytt -f-
key: true


$ echo 'key: yes' | ytt -f- -s
Error: Unmarshaling YAML template 'stdin.yml': yaml: Strict parsing: Found 'yes' ambigious (could be !!str or !!bool)

To fix error, explicitly make it a string:

$ echo 'key: "yes"' | ytt -f- -s
key: "yes"

or via YAML tag !!str:

$ echo 'key: !!str yes' | ytt -f- -s
key: "yes"

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