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Windows Help file (.hlp)

.hlp file signature | application/winhlp

Windows Help (HLP) is a legacy help file format developed by Microsoft for early versions of Windows. It was used to store application help content, including topic text, links, and navigation features, and was commonly opened by the Windows Help viewer and software installers. Because it is an older format replaced by later help systems, HLP files may require compatibility tools on modern Windows versions; files from untrusted sources should still be handled cautiously.

Safe

Magic Bytes

Offset 0
3F 5F

Sources: Wikipedia

All Known Signatures

4 signature variants are documented for .hlp files across multiple sources.

Hex Signature Offset Sources
3F 5F 0 Wikipedia
00 00 FF FF FF FF 6 Gary Kessler
3F 5F 03 00 0 Gary Kessler
4C 4E 02 00 0 Gary Kessler

Extension

.hlp

MIME Type

application/winhlp

Byte Offset

0

Risk Level

Safe

Validation Code

How to validate .hlp files in Python

Python 
def is_hlp(file_path: str) -> bool:
    """Check if file is a valid HLP by magic bytes."""
    signature = bytes([0x3F, 0x5F])
    with open(file_path, "rb") as f:
        return f.read(2) == signature

How to validate .hlp files in Node.js

Node.js 
function isHLP(buffer: Buffer): boolean {
  const signature = Buffer.from([0x3F, 0x5F]);
  return buffer.subarray(0, 2).equals(signature);
}

How to validate .hlp files in Go

Go 
func IsHLP(data []byte) bool {
    signature := []byte{0x3F, 0x5F}
    if len(data) < 2 {
        return false
    }
    return bytes.Equal(data[:2], signature)
}

API Endpoint

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

See the full API documentation for all endpoints and parameters.

Frequently Asked Questions

What is a .hlp file?

A .hlp file is a Windows Help file file. Windows Help (HLP) is a legacy help file format developed by Microsoft for early versions of Windows. It was used to store application help content, including topic text, links, and navigation features, and was commonly opened by the Windows Help viewer and software installers. Because it is an older format replaced by later help systems, HLP files may require compatibility tools on modern Windows versions; files from untrusted sources should still be handled cautiously.

What are the magic bytes for .hlp files?

The magic bytes for Windows Help file files are 3F 5F at byte offset 0. These bytes uniquely identify the file format regardless of the file extension.

How do I validate a .hlp file?

To validate a .hlp file, read the first bytes of the file and compare them against the known magic bytes (3F 5F) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.

What is the MIME type for .hlp files?

The primary MIME type for .hlp files is application/winhlp.

Is it safe to open .hlp files?

Windows Help file (.hlp) 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.