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Windows NT Registry and Registry Undo files (.reg)

.reg file signature | application/octet-stream

Windows NT Registry and Registry Undo files

Safe

Magic Bytes

Offset 0
52 45 47 45 44 49 54

Sources: Gary Kessler

All Known Signatures

2 signature variants are documented for .reg files across multiple sources.

Hex Signature Offset Sources
52 45 47 45 44 49 54 0 Gary Kessler
FF FE 0 Gary Kessler

Extension

.reg

MIME Type

application/octet-stream

Byte Offset

0

Risk Level

Safe

Validation Code

How to validate .reg files in Python

Python 
def is_reg(file_path: str) -> bool:
    """Check if file is a valid REG by magic bytes."""
    signature = bytes([0x52, 0x45, 0x47, 0x45, 0x44, 0x49, 0x54])
    with open(file_path, "rb") as f:
        return f.read(7) == signature

How to validate .reg files in Node.js

Node.js 
function isREG(buffer: Buffer): boolean {
  const signature = Buffer.from([0x52, 0x45, 0x47, 0x45, 0x44, 0x49, 0x54]);
  return buffer.subarray(0, 7).equals(signature);
}

How to validate .reg files in Go

Go 
func IsREG(data []byte) bool {
    signature := []byte{0x52, 0x45, 0x47, 0x45, 0x44, 0x49, 0x54}
    if len(data) < 7 {
        return false
    }
    return bytes.Equal(data[:7], signature)
}

API Endpoint

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

See the full API documentation for all endpoints and parameters.

Frequently Asked Questions

What is a .reg file?

A .reg file is a Windows NT Registry and Registry Undo files file. Windows NT Registry and Registry Undo files

What are the magic bytes for .reg files?

The magic bytes for Windows NT Registry and Registry Undo files files are 52 45 47 45 44 49 54 at byte offset 0. These bytes uniquely identify the file format regardless of the file extension.

How do I validate a .reg file?

To validate a .reg file, read the first bytes of the file and compare them against the known magic bytes (52 45 47 45 44 49 54) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.

What is the MIME type for .reg files?

There is no officially registered MIME type for .reg files. Systems typically use application/octet-stream as a generic fallback when handling this format.

Is it safe to open .reg files?

Windows NT Registry and Registry Undo files (.reg) 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.