invalid previewer specification: %#v with error: no prefix i

Error message

invalid previewer specification: %#v with error: no prefix in pattern specification

What it means

The first shell word of the previewer spec did not contain a ':' separating the prefix (name or mime) from the pattern. Kitty requires the spec to start with 'prefix:pattern'.

Source

Thrown at kittens/choose_files/main.go:304

	q := utils.IfElse(p.use_mimetype, mt, fname)
	matched, err := filepath.Match(p.pattern, q)
	return matched && err == nil
}

var previewers []previewer

func load_previewers(cfg *Config) (err error) {
	for _, spec := range cfg.Previewer {
		parts, err := shlex.Split(spec)
		if err != nil {
			return fmt.Errorf("invalid previewer specification: %#v with error: %w", spec, err)
		}
		if len(parts) < 2 {
			return fmt.Errorf("invalid previewer specification: %#v with error: no command specified", spec)
		}
		prefix, pattern, found := strings.Cut(parts[0], ":")
		if !found {
			return fmt.Errorf("invalid previewer specification: %#v with error: no prefix in pattern specification", spec)
		}
		previewers = append(previewers, previewer{parts[1:], pattern, prefix == "mime"})
	}
	return
}

func load_config(opts *Options) (ans *Config, err error) {
	ans = NewConfig()
	p := config.ConfigParser{LineHandler: ans.Parse}
	err = p.LoadConfig("choose-files.conf", opts.Config, opts.Override)
	if err != nil {
		return nil, err
	}
	ans.KeyboardShortcuts = config.ResolveShortcuts(ans.KeyboardShortcuts)
	parts, err := shlex.Split(ans.Video_preview)
	if err != nil {
		return nil, err
	}

View on GitHub (pinned to 6d5d0c4406)

Solutions

Prefix the pattern: use 'mime:image/*' or 'name:*.png' as the first token
Consult kitty docs for the exact previewer spec grammar

Example fix

# before
--previewer '*.png chafa {file}'
# after
--previewer 'name:*.png chafa {file}'

Defensive patterns

Strategy: validation

Validate before calling

if _, _, ok := strings.Cut(parts[0], ":"); !ok { /* reject spec: missing prefix */ }

Prevention

Always start specs with name: or mime:
Document the expected grammar next to your config

When it happens

Trigger: Passing a spec whose first token is only a pattern, e.g. --previewer '*.png mycommand', with no 'name:' or 'mime:' prefix.

Common situations: Forgetting the mime:/name: qualifier; assuming glob-only syntax from other tools (fzf-style).

Related errors

AI-assisted analysis of kovidgoyal/kitty@6d5d0c4406 (2026-08-27). Data as JSON: /api/errors/db17c1d66ccecc41. Report an issue: GitHub.