Microsoft Office Open XML Format magic bytes (.xlsx)
.xlsx file signature: 50 4B 03 04 | application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
Category: Office
Microsoft Excel Spreadsheet (XLSX) is a spreadsheet file format based on the Microsoft Office Open XML standard, developed by Microsoft and standardized by Ecma International and ISO/IEC. It is used for worksheets, tables, formulas, charts, and business data exchange in Microsoft Excel and compatible office applications. The format is generally safe, but like other document containers it can include macros in related formats or embedded content from untrusted sources.
Magic Bytes
Offset 0
50 4B 03 04
Sources: Wikipedia
All Known Signatures
4 signature variants are documented for .xlsx files across multiple sources.
| Hex Signature | Offset | Sources |
|---|---|---|
| 50 4B 03 04 | 0 | Wikipedia |
| 50 4B 05 06 | 0 | Wikipedia |
| 50 4B 07 08 | 0 | Wikipedia |
| 50 4B 03 04 14 00 06 00 | 0 | Gary Kessler |
Validation Code
How to validate .xlsx files in Python
def is_xlsx(file_path: str) -> bool:
"""Check if file is a valid XLSX by magic bytes."""
signature = bytes([0x50, 0x4B, 0x03, 0x04])
with open(file_path, "rb") as f:
return f.read(4) == signatureHow to validate .xlsx files in Node.js
function isXLSX(buffer: Buffer): boolean {
const signature = Buffer.from([0x50, 0x4B, 0x03, 0x04]);
return buffer.subarray(0, 4).equals(signature);
}How to validate .xlsx files in Go
func IsXLSX(data []byte) bool {
signature := []byte{0x50, 0x4B, 0x03, 0x04}
if len(data) < 4 {
return false
}
return bytes.Equal(data[:4], signature)
}API Endpoint
/api/v1/xlsx
curl https://filesignature.org/api/v1/xlsx
See the full API documentation for all endpoints and parameters.
Related Formats
Frequently Asked Questions
What is a .xlsx file?
A .xlsx file is a Microsoft Office Open XML Format. Microsoft Excel Spreadsheet (XLSX) is a spreadsheet file format based on the Microsoft Office Open XML standard, developed by Microsoft and standardized by Ecma International and ISO/IEC. It is used for worksheets, tables, formulas, charts, and business data exchange in Microsoft Excel and compatible office applications. The format is generally safe, but like other document containers it can include macros in related formats or embedded content from untrusted sources.
What are the magic bytes for .xlsx files?
The magic bytes for Microsoft Office Open XML Format (.xlsx) files are 50 4B 03 04 at byte offset 0. These bytes identify the file format more reliably than the extension alone.
How do I validate a .xlsx file?
To validate a .xlsx file, read the first bytes of the file and compare them against the known magic bytes (50 4B 03 04) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.
What is the MIME type for .xlsx files?
The primary MIME type for .xlsx files is application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.
Is it safe to open .xlsx files?
Microsoft Office Open XML Format (.xlsx) 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.