gohugoio/hugo · error

invalid strict mode; expected one of error, ignore, or warn;

Error message

invalid strict mode; expected one of error, ignore, or warn; received %s

What it means

`transform.ToMath` renders LaTeX with KaTeX and accepts an options map including `strict`, which controls how KaTeX handles non-standard LaTeX. Hugo validates that `strict` is exactly `error` (the default), `ignore`, or `warn`, and rejects any other value after weak-decoding the options.

Source

Thrown at tpl/transform/transform.go:287

			Output:           "mathml",
			MinRuleThickness: 0.04,
			ErrorColor:       "#cc0000",
			ThrowOnError:     true,
			Strict:           "error",
		},
	}

	if len(args) > 1 {
		if err := mapstructure.WeakDecode(args[1], &katexInput.Options); err != nil {
			return "", err
		}
	}

	switch katexInput.Options.Strict {
	case "error", "ignore", "warn":
		// Valid strict mode, continue
	default:
		return "", fmt.Errorf("invalid strict mode; expected one of error, ignore, or warn; received %s", katexInput.Options.Strict)
	}

	type fileCacheEntry struct {
		Version  string   `json:"version"`
		Output   string   `json:"output"`
		Warnings []string `json:"warnings,omitempty"`
	}

	const fileCacheEntryVersion = "v1" // Increment on incompatible changes.

	s := hashing.HashString(args...)
	key := "tomath/" + fileCacheEntryVersion + "/" + s[:2] + "/" + s[2:]
	fileCache := ns.deps.ResourceSpec.FileCaches.MiscCache()

	v, err := ns.cacheMath.GetOrCreate(key, func(string) (template.HTML, error) {
		_, r, err := fileCache.GetOrCreate(key, func() (io.ReadCloser, error) {
			message := warpc.Message[warpc.KatexInput]{
				Header: warpc.Header{

View on GitHub ↗ (pinned to 8a468df065)

Solutions

1. Set strict to one of the exact strings: `error`, `ignore`, or `warn`.
2. Translate boolean intent: `strict: false` in KaTeX JS ≈ `"ignore"`; `strict: true` ≈ `"error"`.
3. Omit the option to keep the default `error` mode.

Example fix

<!-- before -->
{{ transform.ToMath .Inner (dict "strict" false) }}
<!-- after -->
{{ transform.ToMath .Inner (dict "strict" "ignore") }}

{{ $strict := .Params.strictMode | default "error" }}
{{ if not (in (slice "error" "ignore" "warn") $strict) }}
  {{ errorf "strict must be error|ignore|warn, got %q" $strict }}
{{ end }}
{{ $out := transform.ToMath $expr (dict "strict" $strict) }}

When it happens

Trigger: Calling `{{ transform.ToMath $expr (dict "strict" "true") }}` or any `strict` value outside error/ignore/warn — e.g. booleans, `"strict"`, `"off"`, or KaTeX-JS function-style values.

Common situations: Assuming `strict` is a boolean like in KaTeX's JS API (where `strict: false` is valid); typos or capitalized values; copying KaTeX docs that use a handler function, which Hugo's embedded KaTeX doesn't accept.

Related errors

• failed to detect format from content
• failed to detect target data serialization format
• invalid options type: %w
• failed to decode options: %w
• invalid character: %q

AI-assisted analysis of gohugoio/hugo@8a468df065 (2026-07-31). Data as JSON: /data/errors/0b294f88d8fda15e.json. Report an issue: GitHub ↗.