MHTML (.mhtml)

.mhtml file signature | multipart/related

MHTML (MIME HTML) is a web archive format standardized by the IETF and supported by web browsers and email clients to package an HTML document with its related resources in a single file. It is used for saving complete web pages, distributing archived content, and exchanging message-based HTML documents. Because it can include embedded resources and active content, files from untrusted sources should be opened with caution; the format is now largely legacy.

Safe

Magic Bytes

Offset 0


              4D 49 4D 45 2D 56 65 72 73 69 6F 6E 3A 20 31 2E 30

Sources: Apache Tika

Extension

.mhtml

MIME Type

multipart/related

Byte Offset

Risk Level

Safe

Validation Code

How to validate .mhtml files in Python

Python

def is_mhtml(file_path: str) -> bool:
    """Check if file is a valid MHTML by magic bytes."""
    signature = bytes([0x4D, 0x49, 0x4D, 0x45, 0x2D, 0x56, 0x65, 0x72, 0x73, 0x69, 0x6F, 0x6E, 0x3A, 0x20, 0x31, 0x2E, 0x30])
    with open(file_path, "rb") as f:
        return f.read(17) == signature

How to validate .mhtml files in Node.js

Node.js

function isMHTML(buffer: Buffer): boolean {
  const signature = Buffer.from([0x4D, 0x49, 0x4D, 0x45, 0x2D, 0x56, 0x65, 0x72, 0x73, 0x69, 0x6F, 0x6E, 0x3A, 0x20, 0x31, 0x2E, 0x30]);
  return buffer.subarray(0, 17).equals(signature);
}

How to validate .mhtml files in Go

func IsMHTML(data []byte) bool {
    signature := []byte{0x4D, 0x49, 0x4D, 0x45, 0x2D, 0x56, 0x65, 0x72, 0x73, 0x69, 0x6F, 0x6E, 0x3A, 0x20, 0x31, 0x2E, 0x30}
    if len(data) < 17 {
        return false
    }
    return bytes.Equal(data[:17], signature)
}

API Endpoint

GET /api/v1/mhtml


              curl https://filesignature.org/api/v1/mhtml

See the full API documentation for all endpoints and parameters.

Related Formats

.mht

Frequently Asked Questions

What is a .mhtml file?

A .mhtml file is identified by the magic bytes 4D 49 4D 45 2D 56 65 72 73 69 6F 6E 3A 20 31 2E 30 at byte offset 0. MHTML (MIME HTML) is a web archive format standardized by the IETF and supported by web browsers and email clients to package an HTML document with its related resources in a single file. It is used for saving complete web pages, distributing archived content, and exchanging message-based HTML documents. Because it can include embedded resources and active content, files from untrusted sources should be opened with caution; the format is now largely legacy.

What are the magic bytes for .mhtml files?

The magic bytes for MHTML files are 4D 49 4D 45 2D 56 65 72 73 69 6F 6E 3A 20 31 2E 30 at byte offset 0. These bytes uniquely identify the file format regardless of the file extension.

How do I validate a .mhtml file?

To validate a .mhtml file, read the first bytes of the file and compare them against the known magic bytes (4D 49 4D 45 2D 56 65 72 73 69 6F 6E 3A 20 31 2E 30) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.

What is the MIME type for .mhtml files?

The primary MIME type for .mhtml files is multipart/related.

Is it safe to open .mhtml files?

MHTML (.mhtml) 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.