kovidgoyal/kitty · warning

The font specification %s is invalid as %s does not contain

Error message

The font specification %s is invalid as %s does not contain an =

What it means

The choose_fonts kitten parses a font specification string (e.g. 'family=Mono style=Bold') by splitting it into items and cutting each on '='. If an item has no '=' separator, the specification is rejected. This is a config-parsing error for user-supplied font strings.

Source

Thrown at kittens/choose_fonts/types.go:300

}

func NewFontSpec(spec string, features map[string]FeatureData) (ans FontSpec, err error) {
	if spec == "" || spec == "auto" {
		ans.system = settable_string{"auto", true}
		return
	}
	parts, err := shlex.Split(spec)
	if err != nil {
		return
	}
	if !strings.Contains(parts[0], "=") {
		ans.system = settable_string{spec, true}
		return
	}
	for _, item := range parts {
		k, v, found := strings.Cut(item, "=")
		if !found {
			return ans, fmt.Errorf("The font specification %s is invalid as %s does not contain an =", spec, item)
		}
		switch k {
		case "family":
			ans.family = settable_string{v, true}
		case "style":
			ans.style = settable_string{v, true}
		case "full_name":
			ans.full_name = settable_string{v, true}
		case "postscript_name":
			ans.postscript_name = settable_string{v, true}
		case "variable_name":
			ans.variable_name = settable_string{v, true}
		case "features":
			for _, x := range utils.NewSeparatorScanner(v, " ").Split(v) {
				pff, err := NewParsedFontFeature(x, features)
				if err != nil {
					return ans, err
				}

View on GitHub (pinned to 6d5d0c4406)

Solutions

1. Rewrite the spec as key=value pairs, e.g. 'family=JetBrains Mono style=Bold'
2. Quote the whole spec so the shell doesn't split it into stray items
3. Check for stray commas/spaces that create standalone tokens without '='

Example fix

// before
spec := "JetBrains Mono"
// after
spec := "family=JetBrains Mono"

func validFontSpec(spec string) bool {
	for _, item := range strings.Fields(spec) {
		if _, _, ok := strings.Cut(item, "="); !ok {
			return false
		}
	}
	return true
}

if err := parseFontSpec(spec); err != nil { log.Printf("bad font spec %q: %v", spec, err) }

When it happens

Trigger: Calling the font specification parser with a spec like 'Mono' or 'Mono Bold' where an item lacks key=value form; passing a malformed --font-spec / font family string to the choose_fonts kitten.

Common situations: Typing a bare font family name instead of 'family=Name', forgetting the '=' in 'style=Bold', extra spaces producing items like 'Bold' without a key.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

• Warning: unable to parse dircolors line "{line}"
• must have codepoints AND font name
• Failed to find the kitty executable, this kitten requires th
• Trying to send data when to pipe is nil
• Could not encode message to kitty with error: %w

AI-assisted analysis of kovidgoyal/kitty@6d5d0c4406 (2026-08-27). Data as JSON: /api/errors/5c25604dd9041a90. Report an issue: GitHub.