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Lotus 1-2-3 spreadsheet (.wk3)

.wk3 file signature | application/vnd.lotus-1-2-3;version=3

Lotus 1-2-3 spreadsheet (v3) file

Safe

Magic Bytes

Offset 0
00 00 1A 00 00 10 04 00 00 00 00 00

Sources: Wikipedia, Gary Kessler

All Known Signatures

3 signature variants are documented for .wk3 files across multiple sources.

Hex Signature Offset Sources
00 00 1A 00 00 10 04 00 00 00 00 00 0 Wikipedia, Gary Kessler
00 00 1A 00 00 10 04 00 0 Apache Tika
00 00 03 F3 0 Gary Kessler

Extension

.wk3

MIME Type

application/vnd.lotus-1-2-3;version=3

Byte Offset

0

Risk Level

Safe

Validation Code

How to validate .wk3 files in Python

Python 
def is_wk3(file_path: str) -> bool:
    """Check if file is a valid WK3 by magic bytes."""
    signature = bytes([0x00, 0x00, 0x1A, 0x00, 0x00, 0x10, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00])
    with open(file_path, "rb") as f:
        return f.read(12) == signature

How to validate .wk3 files in Node.js

Node.js 
function isWK3(buffer: Buffer): boolean {
  const signature = Buffer.from([0x00, 0x00, 0x1A, 0x00, 0x00, 0x10, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00]);
  return buffer.subarray(0, 12).equals(signature);
}

How to validate .wk3 files in Go

Go 
func IsWK3(data []byte) bool {
    signature := []byte{0x00, 0x00, 0x1A, 0x00, 0x00, 0x10, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00}
    if len(data) < 12 {
        return false
    }
    return bytes.Equal(data[:12], signature)
}

API Endpoint

GET /api/v1/wk3
curl https://filesignature.org/api/v1/wk3

See the full API documentation for all endpoints and parameters.

Frequently Asked Questions

What is a .wk3 file?

A .wk3 file is a Lotus 1-2-3 spreadsheet file. Lotus 1-2-3 spreadsheet (v3) file

What are the magic bytes for .wk3 files?

The magic bytes for Lotus 1-2-3 spreadsheet files are 00 00 1A 00 00 10 04 00 00 00 00 00 at byte offset 0. These bytes uniquely identify the file format regardless of the file extension.

How do I validate a .wk3 file?

To validate a .wk3 file, read the first bytes of the file and compare them against the known magic bytes (00 00 1A 00 00 10 04 00 00 00 00 00) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.

What is the MIME type for .wk3 files?

The primary MIME type for .wk3 files is application/vnd.lotus-1-2-3;version=3.

Is it safe to open .wk3 files?

Lotus 1-2-3 spreadsheet (.wk3) 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.