mikefarah/yq · error

cannot encode %v as base64, can only operate on strings

Error message

cannot encode %v as base64, can only operate on strings

What it means

Encode was asked to base64-encode a node whose resolved tag is not !!str (e.g. a map, sequence, or number). The base64 encoder is a string-only transform — it takes the node's scalar text and encodes it — so any non-string node is rejected up front by this tag guard.

Source

Thrown at pkg/yqlib/encoder_base64.go:33

func NewBase64Encoder() Encoder {
	return &base64Encoder{encoding: *base64.StdEncoding}
}

func (e *base64Encoder) CanHandleAliases() bool {
	return false
}

func (e *base64Encoder) PrintDocumentSeparator(_ io.Writer) error {
	return nil
}

func (e *base64Encoder) PrintLeadingContent(_ io.Writer, _ string) error {
	return nil
}

func (e *base64Encoder) Encode(writer io.Writer, node *CandidateNode) error {
	if node.guessTagFromCustomType() != "!!str" {
		return fmt.Errorf("cannot encode %v as base64, can only operate on strings", node.Tag)
	}
	_, err := writer.Write([]byte(e.encoding.EncodeToString([]byte(node.Value))))
	return err
}

View on GitHub (pinned to 8b5af0694b)

Solutions

1. Convert the value to a string first, e.g. ... | tostring | @base64
2. Select a scalar string field instead of a whole map/array
3. Use tostring on numbers/booleans before encoding

When it happens

Trigger: Thrown at pkg/yqlib/encoder_base64.go:33 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of mikefarah/yq@8b5af0694b (2026-09-05). Data as JSON: /api/errors/20d17582f38afe44. Report an issue: GitHub.