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ZLIB (.zlib)

.zlib file signature | application/octet-stream

ZLIB is a lossless data compression format and software library originally created by Jean-loup Gailly and Mark Adler, and maintained through the zlib project. It is commonly used in network protocols, PNG images, HTTP content encoding, and many applications that need compact, streamable data storage or transmission. The format is long-established and generally safe, though compressed data from untrusted sources can be used in decompression-bomb attacks or to consume excessive memory and CPU.

Safe

Magic Bytes

Offset 0
78 01

Sources: Wikipedia

Extension

.zlib

MIME Type

application/octet-stream

Byte Offset

0

Risk Level

Safe

Validation Code

How to validate .zlib files in Python

Python 
def is_zlib(file_path: str) -> bool:
    """Check if file is a valid ZLIB by magic bytes."""
    signature = bytes([0x78, 0x01])
    with open(file_path, "rb") as f:
        return f.read(2) == signature

How to validate .zlib files in Node.js

Node.js 
function isZLIB(buffer: Buffer): boolean {
  const signature = Buffer.from([0x78, 0x01]);
  return buffer.subarray(0, 2).equals(signature);
}

How to validate .zlib files in Go

Go 
func IsZLIB(data []byte) bool {
    signature := []byte{0x78, 0x01}
    if len(data) < 2 {
        return false
    }
    return bytes.Equal(data[:2], signature)
}

API Endpoint

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

See the full API documentation for all endpoints and parameters.

Frequently Asked Questions

What is a .zlib file?

A .zlib file is identified by the magic bytes 78 01 at byte offset 0. ZLIB is a lossless data compression format and software library originally created by Jean-loup Gailly and Mark Adler, and maintained through the zlib project. It is commonly used in network protocols, PNG images, HTTP content encoding, and many applications that need compact, streamable data storage or transmission. The format is long-established and generally safe, though compressed data from untrusted sources can be used in decompression-bomb attacks or to consume excessive memory and CPU.

What are the magic bytes for .zlib files?

The magic bytes for ZLIB files are 78 01 at byte offset 0. These bytes uniquely identify the file format regardless of the file extension.

How do I validate a .zlib file?

To validate a .zlib file, read the first bytes of the file and compare them against the known magic bytes (78 01) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.

What is the MIME type for .zlib files?

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

Is it safe to open .zlib files?

ZLIB (.zlib) 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.