Files without extensions are those whose filenames end without a dot (.) and additional characters (like .txt or .jpg), or where the dot is simply the last character in the name. Unlike standard files that use extensions to signal their format (e.g., .pdf for documents), these files rely solely on internal metadata or context for identification. Operating systems and applications might not automatically recognize their type.

System administrators often encounter such files in core configurations; for example, Linux/Unix hosts files (/etc/hosts) and important Windows system files like NTLDR (historically) lack extensions. Software developers also frequently use extension-less files, such as Dockerfile or .env for environment variables, where the lack of extension aids command-line tooling or prevents inadvertent opening. Git configuration files (gitconfig) are another common instance.

While omitting extensions can enhance security by obscuring file types, it hinders users and software from easily identifying the content or compatible applications. This necessitates manual inspection or specialized tools, reducing search efficiency. Developers should use caution with critical configuration files without extensions, ensuring their purpose is well-documented to avoid confusion during maintenance or troubleshooting.