charmbracelet/glow · error

' ' is not a supported configuration type: use ' ' or

Error message

'%s' is not a supported configuration type: use '%s' or '%s'

What it means

ensureConfigFile enforces that the configuration filename ends in .yaml or .yml, rejecting anything else via path.Ext. The check applies to the --config value when passed, otherwise to Viper's ConfigFileUsed(). Glow deliberately restricts Viper's broader format support to YAML for its config.

Solutions

1. Rename the file to end in .yml or .yaml
2. If you wanted JSON/TOML config, convert it to YAML — glow only accepts YAML
3. Check for stray suffixes: glow.yml.example must become glow.yml

Example fix

# before
$ glow config --config ~/.config/glow/glow.json
# Error: '.json' is not a supported configuration type: use '.yaml' or '.yml'

# after
$ mv ~/.config/glow/glow.json ~/.config/glow/glow.yml && glow config --config ~/.config/glow/glow.yml

func validConfigExt(p string) error {
	ext := path.Ext(p)
	if ext != ".yaml" && ext != ".yml" {
		return fmt.Errorf("%s: glow config must end in .yaml or .yml", p)
	}
	return nil
}

if err := validConfigExt(cfgPath); err != nil {
	cfgPath = strings.TrimSuffix(cfgPath, path.Ext(cfgPath)) + ".yml"
}

if err := ensureConfigFile(); err != nil {
	var extErr *unsupportedConfigTypeError // wrap it in your own sentinel if vendoring
	if errors.As(err, &extErr) || strings.Contains(err.Error(), "not a supported configuration type") {
		// rename to .yml and retry once
		_ = os.Rename(badPath, strings.TrimSuffix(badPath, path.Ext(badPath))+".yml")
		return ensureConfigFile()
	}
	return err
}

When it happens

Trigger: Passing glow config --config settings.json (or .toml, .txt, or no extension); a config file discovered by Viper with a non-YAML extension; a typo like glow.yam or config.yaml.bak.

Common situations: Users migrating configs from tools that use JSON/TOML; backup files with extra suffixes; scripts generating the config path with a wrong template.

Related errors

• cannot use both pager and tui
• could not write configuration file
• error parsing config
• invalid url
• invalid url

AI-assisted analysis of charmbracelet/glow@e3970c813d (2026-08-15). Data as JSON: /api/errors/0762a76d29460892. Report an issue: GitHub.

Appendix: source

Thrown at config_cmd.go:65

		if err := c.Run(); err != nil {
			return fmt.Errorf("unable to run command: %w", err)
		}

		fmt.Println("Wrote config file to:", configFile)
		return nil
	},
}

func ensureConfigFile() error {
	if configFile == "" {
		configFile = viper.GetViper().ConfigFileUsed()
		if err := os.MkdirAll(filepath.Dir(configFile), 0o755); err != nil { //nolint:gosec
			return fmt.Errorf("could not write configuration file: %w", err)
		}
	}

	if ext := path.Ext(configFile); ext != ".yaml" && ext != ".yml" {
		return fmt.Errorf("'%s' is not a supported configuration type: use '%s' or '%s'", ext, ".yaml", ".yml")
	}

	if _, err := os.Stat(configFile); errors.Is(err, fs.ErrNotExist) {
		// File doesn't exist yet, create all necessary directories and
		// write the default config file
		if err := os.MkdirAll(filepath.Dir(configFile), 0o700); err != nil {
			return fmt.Errorf("unable create directory: %w", err)
		}

		f, err := os.Create(configFile)
		if err != nil {
			return fmt.Errorf("unable to create config file: %w", err)
		}
		defer func() { _ = f.Close() }()

		if _, err := f.WriteString(defaultConfig); err != nil {
			return fmt.Errorf("unable to write config file: %w", err)
		}

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