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XML User Interface Language file (.xul)

.xul file signature | application/vnd.mozilla.xul+xml

XML User Interface Language (XUL) is an XML-based user interface markup language created by Mozilla for defining application chrome and desktop-style interfaces. It was used primarily in Mozilla applications and related extensions to describe windows, menus, toolbars, and dialogs, especially in the Firefox and Thunderbird codebase. XUL is a legacy technology in most modern Mozilla projects, and files are generally safe to inspect as plain XML, though they may reference scripts or resources.

Safe

Magic Bytes

Offset 0
3C 3F 78 6D 6C 20 76 65 72 73 69 6F 6E 3D 22 31 2E 30 22 3F 3E

Sources: Gary Kessler

Extension

.xul

MIME Type

application/vnd.mozilla.xul+xml

Byte Offset

0

Risk Level

Safe

Validation Code

How to validate .xul files in Python

Python 
def is_xul(file_path: str) -> bool:
    """Check if file is a valid XUL by magic bytes."""
    signature = bytes([0x3C, 0x3F, 0x78, 0x6D, 0x6C, 0x20, 0x76, 0x65, 0x72, 0x73, 0x69, 0x6F, 0x6E, 0x3D, 0x22, 0x31, 0x2E, 0x30, 0x22, 0x3F, 0x3E])
    with open(file_path, "rb") as f:
        return f.read(21) == signature

How to validate .xul files in Node.js

Node.js 
function isXUL(buffer: Buffer): boolean {
  const signature = Buffer.from([0x3C, 0x3F, 0x78, 0x6D, 0x6C, 0x20, 0x76, 0x65, 0x72, 0x73, 0x69, 0x6F, 0x6E, 0x3D, 0x22, 0x31, 0x2E, 0x30, 0x22, 0x3F, 0x3E]);
  return buffer.subarray(0, 21).equals(signature);
}

How to validate .xul files in Go

Go 
func IsXUL(data []byte) bool {
    signature := []byte{0x3C, 0x3F, 0x78, 0x6D, 0x6C, 0x20, 0x76, 0x65, 0x72, 0x73, 0x69, 0x6F, 0x6E, 0x3D, 0x22, 0x31, 0x2E, 0x30, 0x22, 0x3F, 0x3E}
    if len(data) < 21 {
        return false
    }
    return bytes.Equal(data[:21], signature)
}

API Endpoint

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

See the full API documentation for all endpoints and parameters.

Related Formats

.manifest .xml .msc .other .xsd .xsl

Frequently Asked Questions

What is a .xul file?

A .xul file is a XML User Interface Language file file. XML User Interface Language (XUL) is an XML-based user interface markup language created by Mozilla for defining application chrome and desktop-style interfaces. It was used primarily in Mozilla applications and related extensions to describe windows, menus, toolbars, and dialogs, especially in the Firefox and Thunderbird codebase. XUL is a legacy technology in most modern Mozilla projects, and files are generally safe to inspect as plain XML, though they may reference scripts or resources.

What are the magic bytes for .xul files?

The magic bytes for XML User Interface Language file files are 3C 3F 78 6D 6C 20 76 65 72 73 69 6F 6E 3D 22 31 2E 30 22 3F 3E at byte offset 0. These bytes uniquely identify the file format regardless of the file extension.

How do I validate a .xul file?

To validate a .xul file, read the first bytes of the file and compare them against the known magic bytes (3C 3F 78 6D 6C 20 76 65 72 73 69 6F 6E 3D 22 31 2E 30 22 3F 3E) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.

What is the MIME type for .xul files?

The primary MIME type for .xul files is application/vnd.mozilla.xul+xml.

Is it safe to open .xul files?

XML User Interface Language file (.xul) 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.