What is the README file format?
A .readme file is a plain-text documentation file following the README convention of Unix and open-source software culture. The .readme extension is an uncommon variant of the traditional uppercase README (no extension) and README.txt forms.
README files provide human-readable introductory documentation for a software package, project, or archive. Typical content includes a project description, installation and usage instructions, author information, and a license notice. There is no mandatory structure - content is free-form prose and lists.
The uppercase README with no extension dates to at least the 1970s in Unix distributions, where it was conventionally the first file a user was expected to read; package managers and directory listings often displayed it automatically. README.txt became common on Windows. Since approximately 2008, README.md (Markdown) has become the dominant form because GitHub automatically renders Markdown on repository pages.
The .readme extension is occasionally found in older shareware distributions and certain package managers but carries no technical distinction from .txt - both are plain text that any editor opens without configuration. Encoding is typically UTF-8 (modern) or ASCII (legacy); Windows tools may produce UTF-16 LE files with a BOM, but UTF-8 is standard. File size is almost always under 100 KB.
Security & safety
RISK: LOWPlain text file; no executable code; completely safe to open in any text editor.
Format details
in a nutshellPrograms that open README files
Windows3 apps
Windows Notepad
Built-in Double-click may not work (OS may not recognize .readme extension); right-click → Open With → Notepad. 
macOS2 apps
Linux2 apps
Technical details
deep spec| Encoding | UTF-8 (modern standard); ASCII (legacy); occasionally UTF-16 LE with BOM on Windows |
| Container | Plain text - no binary wrapper, no header, no schema |
| Mandatory structure | None - free-form prose; no defined fields or required order |
| Common filename variants | README (no extension), README.txt, README.md, .readme |
| MIME type | text/plain |
| Typical file size | Almost always under 100 KB |
| Line endings | LF (Unix/macOS/Linux) or CRLF (Windows); both accepted by text editors |
| UTF-8 BOM | Optional - possible on Windows-created files (EF BB BF prefix) |
| Dominant modern form | README.md (Markdown), auto-rendered by GitHub, GitLab, and Bitbucket since ~2008 |
| Historical display | Shown automatically by early Unix directory listings and package managers |
| Associated platforms | All operating systems - Windows, macOS, Linux, Unix |
| Typical content | Project description, installation/usage instructions, author info, license notice |
| Released | 1970s Unix tradition; .readme as a distinct extension less common than plain README or README.txt |
| Latest version | N/A - no versioning |
| Open standard | Yes · royalty-free |
README conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about README files.
