What causes "%v is not a directory" in caddyserver/caddy?

Point listFiles at a directory, e.g. {{ listFiles "/posts" }} or use path.Dir of the file

%v is not a directory

Error message

%v is not a directory

What it means

Returned by the templates module's listFiles function when the path given exists and was opened successfully but is not a directory (stat.IsDir() is false). The function then cannot Readdir it.

Source

Thrown at modules/caddyhttp/templates/tplcontext.go:409

// funcListFiles reads and returns a slice of names from the given
// directory relative to the root of c.
func (c TemplateContext) funcListFiles(name string) ([]string, error) {
	if c.Root == nil {
		return nil, fmt.Errorf("root file system not specified")
	}

	dir, err := c.Root.Open(path.Clean(name))
	if err != nil {
		return nil, err
	}
	defer dir.Close()

	stat, err := dir.Stat()
	if err != nil {
		return nil, err
	}
	if !stat.IsDir() {
		return nil, fmt.Errorf("%v is not a directory", name)
	}

	dirInfo, err := dir.Readdir(0)
	if err != nil {
		return nil, err
	}

	names := make([]string, len(dirInfo))
	for i, fileInfo := range dirInfo {
		names[i] = fileInfo.Name()
	}

	return names, nil
}

// funcFileExists returns true if filename can be opened successfully.
func (c TemplateContext) funcFileExists(filename string) (bool, error) {
	if c.Root == nil {

View on GitHub (pinned to 50e54ee279)

Solutions

Point listFiles at a directory, e.g. {{ listFiles "/posts" }} or use path.Dir of the file
Guard with {{ if (stat .).IsDir }} style checks or split files vs dirs before calling
Log or render the offending path temporarily to see what the placeholder resolves to
Trim trailing filenames from computed paths in the template

Example fix

<!-- before -->
{{ listFiles "/posts/2024/post.md" }}

<!-- after -->
{{ listFiles "/posts/2024" }}

Defensive patterns

Strategy: type-guard

Type guard

{{ $s := stat "/posts/2024" }}{{ if $s.IsDir }}{{ listFiles "/posts/2024" }}{{ else }}not a directory{{ end }}

Prevention

Always stat-check before listFiles when the path is dynamic
Derive directories with path.Dir rather than trusting raw variables
Render candidate paths during development to verify they point at folders

When it happens

Trigger: {{ listFiles "notes.txt" }} where notes.txt is a regular file; or a dynamic path built from a placeholder that resolves to a file name instead of a folder.

Common situations: Passing a file path where a directory was intended, using '.' on a root that maps to a single file, or template logic like {{ listFiles .Path }} where .Path points at an article file rather than its containing directory.

Related errors

AI-assisted analysis of caddyserver/caddy@50e54ee279 (2026-08-15). Data as JSON: /api/errors/7ec4aa12e156a4c9. Report an issue: GitHub.