charmbracelet/gum · error

unable to parse template: %w

Error message

unable to parse template: %w

What it means

Returned by the template formatter when text/template (via the tpl wrapper) cannot Parse the user-supplied template string. This is a compile-time template error: bad syntax, unknown functions, or unbalanced actions. The wrapped error includes the template parser's position information.

Source

Thrown at format/formats.go:60

func markdown(input string, theme string) (string, error) {
	renderer, err := glamour.NewTermRenderer(
		glamour.WithStylePath(theme),
		glamour.WithWordWrap(0),
	)
	if err != nil {
		return "", fmt.Errorf("unable to render: %w", err)
	}
	output, err := renderer.Render(input)
	if err != nil {
		return "", fmt.Errorf("unable to render: %w", err)
	}
	return output, nil
}

func template(input string) (string, error) {
	t, err := tpl.New("tpl").Funcs(templateFuncs()).Parse(input)
	if err != nil {
		return "", fmt.Errorf("unable to parse template: %w", err)
	}

	var buf bytes.Buffer
	err = t.Execute(&buf, nil)
	return buf.String(), err
}

// templateFuncs returns a few useful template helpers for styling text.
func templateFuncs() tpl.FuncMap {
	return tpl.FuncMap{
		"Color": func(values ...any) string {
			s := lipgloss.NewStyle()
			switch len(values) {
			case 2:
				s = s.Foreground(lipgloss.Color(values[0].(string)))
			case 3:
				s = s.
					Foreground(lipgloss.Color(values[0].(string))).

View on GitHub (pinned to 4d089f9550)

Solutions

1. Check template syntax: every {{ }} action must be closed and functions must exist in the template func map
2. Wrap the template in single quotes in the shell so braces are not mangled
3. Only reference available template functions (see templateFuncs in the repo)
4. Remember Execute is called with nil data — do not dereference . fields

Example fix

// before
gum format --type template '{{ .Name | upper'
// after
gum format --type template '{{ upper "hello" }}'

if strings.Count(tpl, "{{") != strings.Count(tpl, "}}") { return fmt.Errorf("unbalanced template braces") }

func isBalancedTemplate(t string) bool { return strings.Count(t, "{{") == strings.Count(t, "}}") }

out, err := format.Format(tpl, format.Template)
if err != nil {
    return fmt.Errorf("template error: %w", err)
}

When it happens

Trigger: Calling Run with Format=template and input containing invalid template syntax such as {{.Field} on a nil-safe template, unknown function names not in templateFuncs(), or unclosed {{ }} actions.

Common situations: Shell interpolation mangling braces; referencing a function that doesn't exist in the template func map; quoting issues causing {{ to be split; data fields referenced although Execute is called with nil data.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• unable to run filter: %w
• not submitted
• failed to run input: %w
• no input provided, see `gum style --help`
• not submitted

AI-assisted analysis of charmbracelet/gum@4d089f9550 (2026-08-31). Data as JSON: /api/errors/47640f72e2ff10d5. Report an issue: GitHub.