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EFI (.efi)

.efi file signature | application/octet-stream

The Extensible Firmware Interface (EFI) file format is an executable image format defined by Intel and later standardized by the UEFI Forum. It is used to load firmware applications, bootloaders, and operating system components in UEFI-based systems. Because EFI files are executable code, they should be obtained from trusted sources; the format is now part of the broader UEFI standard, while the older Intel EFI name is largely historical.

Safe

Magic Bytes

Offset 0
4D 5A

Sources: Wikipedia

Extension

.efi

MIME Type

application/octet-stream

Byte Offset

0

Risk Level

Safe

Validation Code

How to validate .efi files in Python

Python 
def is_efi(file_path: str) -> bool:
    """Check if file is a valid EFI by magic bytes."""
    signature = bytes([0x4D, 0x5A])
    with open(file_path, "rb") as f:
        return f.read(2) == signature

How to validate .efi files in Node.js

Node.js 
function isEFI(buffer: Buffer): boolean {
  const signature = Buffer.from([0x4D, 0x5A]);
  return buffer.subarray(0, 2).equals(signature);
}

How to validate .efi files in Go

Go 
func IsEFI(data []byte) bool {
    signature := []byte{0x4D, 0x5A}
    if len(data) < 2 {
        return false
    }
    return bytes.Equal(data[:2], signature)
}

API Endpoint

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

See the full API documentation for all endpoints and parameters.

Frequently Asked Questions

What is a .efi file?

A .efi file is identified by the magic bytes 4D 5A at byte offset 0. The Extensible Firmware Interface (EFI) file format is an executable image format defined by Intel and later standardized by the UEFI Forum. It is used to load firmware applications, bootloaders, and operating system components in UEFI-based systems. Because EFI files are executable code, they should be obtained from trusted sources; the format is now part of the broader UEFI standard, while the older Intel EFI name is largely historical.

What are the magic bytes for .efi files?

The magic bytes for EFI files are 4D 5A at byte offset 0. These bytes uniquely identify the file format regardless of the file extension.

How do I validate a .efi file?

To validate a .efi file, read the first bytes of the file and compare them against the known magic bytes (4D 5A) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.

What is the MIME type for .efi files?

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

Is it safe to open .efi files?

EFI (.efi) 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.