A POSIX tape archive — an uncompressed sequential-file container.
| 0x00000101 | 7573746172 | ustar | 'ustar' marker in the first header |
TAR concatenates files with 512-byte headers and no compression, which is why it is almost always paired with gzip or xz (.tar.gz, .tar.xz). The 'ustar' marker sits at offset 257 inside the first header, not at the start of the file.
Have a file that might be TAR? Identify it with the File Type Identifier — it reads the magic number locally, nothing is uploaded. Or browse all formats.