gohugoio/hugo · error

failed to detect format from content

Error message

failed to detect format from content

What it means

Thrown by transform.Remarshal when the input data string's format cannot be auto-detected by metadecoders (tpl/transform/remarshal.go:42-44). Remarshal converts between JSON/YAML/TOML; if the source content matches none of these the detector returns empty and the error is raised.

Solutions

1. Ensure the input is valid JSON, YAML, or TOML (test by parsing it standalone first).
2. Pass a map instead of a string so detection is skipped: {{ transform.Remarshal "yaml" (dict "a" 1) }}.
3. Trim/clean the string before passing; remove stray characters.

Example fix

// before
{{ transform.Remarshal "yaml" .RawBody }}
// after
{{ transform.Remarshal "yaml" .Params.config }}

{{/* Validate input parses as JSON/YAML/TOML before Remarshal, or pass a dict */}}
{{ transform.Remarshal "yaml" (dict "a" 1) }}

When it happens

Trigger: Calling {{ transform.Remarshal "yaml" .SomeString }} where .SomeString is malformed or is plain text, CSV, INI, or otherwise not JSON/YAML/TOML.

Common situations: Passing truncated or commented-out front matter; feeding markdown body instead of front matter; encoding the data with an unsupported dialect; whitespace-only or non-ASCII delimiter issues.

Related errors

• failed to detect target data serialization format
• first argument must be a map
• must provide at least one argument
• no Key set in Resource
• transform.Highlight: expects at most 3 arguments

AI-assisted analysis of gohugoio/hugo@52c9bd7908 (2026-08-09). Data as JSON: /api/errors/45d135abf0b3eb20. Report an issue: GitHub.

Appendix: source

Thrown at tpl/transform/remarshal.go:44

		return "", err
	}

	if m, ok := data.(map[string]any); ok {
		meta = m
	} else {
		from, err := cast.ToStringE(data)
		if err != nil {
			return "", err
		}

		from = strings.TrimSpace(from)
		if from == "" {
			return "", nil
		}

		fromFormat := metadecoders.Default.FormatFromContentString(from)
		if fromFormat == "" {
			return "", errors.New("failed to detect format from content")
		}

		meta, err = metadecoders.Default.UnmarshalToMap([]byte(from), fromFormat)
		if err != nil {
			return "", err
		}
	}

	// Make it so 1.0 float64 prints as 1 etc.
	applyMarshalTypes(meta)

	var result bytes.Buffer
	if err := parser.InterfaceToConfig(meta, mark, &result); err != nil {
		return "", err
	}

	return result.String(), nil
}

View on GitHub (pinned to 52c9bd7908)