HDF5 File Signature: 89 48 44 46 0D 0A 1A 0A (Magic Number)

HDF5 files open with an eight-byte signature that mirrors PNG's guard design: the high-bit byte 0x89, the ASCII letters HDF, then CRLF, a DOS end-of-file and a line feed.

What this magic number means

A magic number is a short, fixed run of bytes at a known position that tells a program what a file really is, no matter what the filename says. If a file starts with the bytes 89 48 44 46 0D 0A 1A 0A (the text .HDF....), it is a HDF5 file.

Formats that use the 89 48 44 46 signature

These file types in our database carry this signature:

How to check a file's signature

You can read the first bytes of any file yourself. The magic bytes are shown in hex, the same way this page lists them.

Linux & macOS

xxd -l 16 example.hdf5
hexdump -C -n 16 example.hdf5
file example.hdf5

Windows (PowerShell)

Format-Hex -Path example.hdf5 -Count 16

Python

open("example.hdf5","rb").read(8).hex()

In your browser

Drop the file into the WhatFileType identifier, which reads the signature without uploading it.

Frequently asked questions

What is the HDF5 file signature?

HDF5 files start with the hex bytes 89 48 44 46 0D 0A 1A 0A (.HDF.... in ASCII). This magic number identifies the format regardless of the file's name or extension.

How do I check a file's magic number?

Open the file in a hex editor, or run a command such as xxd -l 16 example.hdf5 on Linux or macOS, or Format-Hex -Path example.hdf5 -Count 16 in Windows PowerShell, and read the first bytes.

Can a file fake the HDF5 signature?

Renaming a file does not change its bytes, so the extension can lie but the signature usually cannot. A genuine HDF5 file has these exact bytes; a file with the wrong bytes is not really HDF5, whatever its name says.

HDF5 file signature