Microsoft Office Open XML Format
application/octet-stream
Magic Bytes
Offset: 0
50 4B 03 04 50 4B 05 06 50 4B 07 08
Microsoft Office Open XML Format (XLSX) is a zip-compressed, XML-based spreadsheet file developed by Microsoft and standardized as ISO/IEC 29500. It serves as the primary format for Microsoft Excel, facilitating data management, complex calculations, and statistical visualization across various software platforms. Superseding the older binary XLS format, XLSX provides improved data integrity and reduced file sizes, though users should exercise caution as related variants can embed macros designed to execute code.
Validation Code
How to validate .xlsx files in Python
Python
def is_xlsx(file_path: str) -> bool:
"""Check if file is a valid XLSX by magic bytes."""
signature = bytes([0x50, 0x4B, 0x03, 0x04, 0x50, 0x4B, 0x05, 0x06, 0x50, 0x4B, 0x07, 0x08])
with open(file_path, "rb") as f:
return f.read(12) == signatureHow to validate .xlsx files in Node.js
Node.js
function isXLSX(buffer: Buffer): boolean {
const signature = Buffer.from([0x50, 0x4B, 0x03, 0x04, 0x50, 0x4B, 0x05, 0x06, 0x50, 0x4B, 0x07, 0x08]);
return buffer.subarray(0, 12).equals(signature);
}
Go
func IsXLSX(data []byte) bool {
signature := []byte{0x50, 0x4B, 0x03, 0x04, 0x50, 0x4B, 0x05, 0x06, 0x50, 0x4B, 0x07, 0x08}
if len(data) < 12 {
return false
}
return bytes.Equal(data[:12], signature)
}API Endpoint
GET
/api/v1/xlsx
curl https://filesignature.org/api/v1/xlsx