Skip to content

CNT (.cnt)

.cnt file signature | application/octet-stream

CNT (Help Contents) is a legacy Windows help index file format developed by Microsoft for the Microsoft Windows 3.x and Windows 95 help system. It stores the table of contents and navigation structure used by help viewers to organize topics, links, and search entries. The format is obsolete and largely replaced by newer help technologies; it is generally safe, though files from untrusted sources should still be handled carefully.

Safe

Magic Bytes

Offset 0
3A 42 61 73 65 20

Sources: Wikipedia

Extension

.cnt

MIME Type

application/octet-stream

Byte Offset

0

Risk Level

Safe

Validation Code

How to validate .cnt files in Python

Python 
def is_cnt(file_path: str) -> bool:
    """Check if file is a valid CNT by magic bytes."""
    signature = bytes([0x3A, 0x42, 0x61, 0x73, 0x65, 0x20])
    with open(file_path, "rb") as f:
        return f.read(6) == signature

How to validate .cnt files in Node.js

Node.js 
function isCNT(buffer: Buffer): boolean {
  const signature = Buffer.from([0x3A, 0x42, 0x61, 0x73, 0x65, 0x20]);
  return buffer.subarray(0, 6).equals(signature);
}

How to validate .cnt files in Go

Go 
func IsCNT(data []byte) bool {
    signature := []byte{0x3A, 0x42, 0x61, 0x73, 0x65, 0x20}
    if len(data) < 6 {
        return false
    }
    return bytes.Equal(data[:6], signature)
}

API Endpoint

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

See the full API documentation for all endpoints and parameters.

Frequently Asked Questions

What is a .cnt file?

A .cnt file is identified by the magic bytes 3A 42 61 73 65 20 at byte offset 0. CNT (Help Contents) is a legacy Windows help index file format developed by Microsoft for the Microsoft Windows 3.x and Windows 95 help system. It stores the table of contents and navigation structure used by help viewers to organize topics, links, and search entries. The format is obsolete and largely replaced by newer help technologies; it is generally safe, though files from untrusted sources should still be handled carefully.

What are the magic bytes for .cnt files?

The magic bytes for CNT files are 3A 42 61 73 65 20 at byte offset 0. These bytes uniquely identify the file format regardless of the file extension.

How do I validate a .cnt file?

To validate a .cnt file, read the first bytes of the file and compare them against the known magic bytes (3A 42 61 73 65 20) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.

What is the MIME type for .cnt files?

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

Is it safe to open .cnt files?

CNT (.cnt) 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.