FAX (.fax)
.fax file signature | application/octet-stream
FAX is a legacy file format for storing facsimile images, originally associated with fax software and maintained through legacy support in some imaging and communication tools. It is used to archive scanned pages, exchange faxed documents, and convert images for transmission or viewing in compatible applications. The format is generally safe, but older files may be limited in compatibility, and any document from an untrusted source should still be handled with standard caution.
Magic Bytes
Offset 0
46 4F 52 4D
Sources: Wikipedia
All Known Signatures
2 signature variants are documented for .fax files across multiple sources.
Extension
.fax
MIME Type
application/octet-stream
Byte Offset
0
Risk Level
Safe
Validation Code
How to validate .fax files in Python
def is_fax(file_path: str) -> bool:
"""Check if file is a valid FAX by magic bytes."""
signature = bytes([0x46, 0x4F, 0x52, 0x4D])
with open(file_path, "rb") as f:
return f.read(4) == signatureHow to validate .fax files in Node.js
function isFAX(buffer: Buffer): boolean {
const signature = Buffer.from([0x46, 0x4F, 0x52, 0x4D]);
return buffer.subarray(0, 4).equals(signature);
}How to validate .fax files in Go
func IsFAX(data []byte) bool {
signature := []byte{0x46, 0x4F, 0x52, 0x4D}
if len(data) < 4 {
return false
}
return bytes.Equal(data[:4], signature)
}API Endpoint
/api/v1/fax
curl https://filesignature.org/api/v1/fax
See the full API documentation for all endpoints and parameters.
Frequently Asked Questions
What is a .fax file?
A .fax file is identified by the magic bytes 46 4F 52 4D at byte offset 0. FAX is a legacy file format for storing facsimile images, originally associated with fax software and maintained through legacy support in some imaging and communication tools. It is used to archive scanned pages, exchange faxed documents, and convert images for transmission or viewing in compatible applications. The format is generally safe, but older files may be limited in compatibility, and any document from an untrusted source should still be handled with standard caution.
What are the magic bytes for .fax files?
The magic bytes for FAX files are 46 4F 52 4D at byte offset 0. These bytes uniquely identify the file format regardless of the file extension.
How do I validate a .fax file?
To validate a .fax file, read the first bytes of the file and compare them against the known magic bytes (46 4F 52 4D) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.
What is the MIME type for .fax files?
There is no officially registered MIME type for .fax files. Systems typically use application/octet-stream as a generic fallback when handling this format.
Is it safe to open .fax files?
FAX (.fax) files are generally safe to open. They are classified as low risk because they primarily contain data rather than executable code. However, always ensure files come from a trusted source.