Executable

WASM WebAssembly Binary

WebAssembly Binary is a executable format commonly identified by .wasm. Use the listed signatures, MIME types, and structure notes to validate files beyond the extension.

Extensions .wasm

MIME application/wasm

Magic numbers

Analyze your file

offset 0 WebAssembly Binary leading signature

00 61 73 6D 01 00 00 00

.asm....

Structure

Magic
Version
Sections

Caveats

Do not trust the extension alone. Check the MIME type, the first bytes such as 00 61 73 6D 01 00 00 00, and format-specific structure when possible.
Container formats and damaged files can share the same opening bytes, so deeper validation may be required for production upload, preview, or conversion flows.

Detection example

SIGNATURE = bytes.fromhex("0061736d01000000")
OFFSET = 0

def is_wasm(path: str) -> bool:
    with open(path, "rb") as f:
        f.seek(OFFSET)
        head = f.read(len(SIGNATURE))
    return head == SIGNATURE

const SIGNATURE = [0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00];
const OFFSET = 0;

// bytes: a Uint8Array / Buffer holding the start of the file
export function isWasm(bytes) {
  return SIGNATURE.every((byte, i) => bytes[OFFSET + i] === byte);
}

package fileid

import "bytes"

var iswasmSignature = []byte{0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00}

const iswasmOffset = 0

func IsWasm(b []byte) bool {
	end := iswasmOffset + len(iswasmSignature)
	if len(b) < end {
		return false
	}
	return bytes.Equal(b[iswasmOffset:end], iswasmSignature)
}

const SIGNATURE: &[u8] = &[0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00];
const OFFSET: usize = 0;

fn is_wasm(bytes: &[u8]) -> bool {
    bytes.get(OFFSET..OFFSET + SIGNATURE.len()) == Some(SIGNATURE)
}

<?php
$signature = "\x00\x61\x73\x6d\x01\x00\x00\x00";
$offset = 0;

function is_wasm(string $bytes): bool {
    global $signature, $offset;
    return substr($bytes, $offset, strlen($signature)) === $signature;
}

Practical usage

Use cases

WebAssembly Binary is used to identify executables, binary modules, distribution artifacts, and upload restrictions. Inspect headers and structure without executing the file.

Common detection mistakes

The .wasm extension alone does not prove the file contents. Upload and conversion flows should combine extension, MIME type, leading bytes, and format-specific structure checks.
WebAssembly Binary can start with signatures such as 00 61 73 6D 01 00 00 00, but related containers and damaged files may require additional validation.

Security notes

Executable formats should be downloaded only for inspection, not execution. Keep analysis isolated and separate extension checks, MIME checks, and execution permissions.

Using samples

11 samples help test leading-byte detection, parser errors, upload limits, and download behavior.

Sample files

11 / 11 files

Search File size

Sample Traits Size Source / license / SHA-256

Exe

Empty WASM Module

Empty WASM Module is a WebAssembly Binary sample generated for file format testing. It can be used to test downloads, parsers, previews, and file type detection.

empty.wasm

Type Sample

Small file

8 B

Generated CC0 1.0

SHA-256 93a44bbb96c751218e4c00d479e4c14358122a389acca16205b1e4d0dc5f9476

Download

Exe

Blue Sky WASM

Blue Sky WASM is a WebAssembly Binary sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.

01-blue-sky.wasm

Type Sample

Small file

189 B

Wikimedia Commons CC0 1.0

SHA-256 bbca15cf7ea4349eb53712512e56e6358efe1f0420f1c8ba0966e125811d4cd8

Download

Exe

Flower Garden WASM

Flower Garden WASM is a WebAssembly Binary sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.

02-flower-garden.wasm

Type Sample

Small file

277 B

Wikimedia Commons CC0 1.0

SHA-256 03691c2ac37a32e591e278c32754f090e1a14633fefccf8adfe1eb5fbbab71e4

Download

Exe

Navy Blue Sky WASM

Navy Blue Sky WASM is a WebAssembly Binary sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.

03-navy-blue-sky.wasm

Type Sample

Small file

291 B

Wikimedia Commons CC0 1.0

SHA-256 007dbf2c46e952cc15c81254b6a9a69d1418f4d0e33e2032f37335c8307423e4

Download

Exe

Nature of the Sky WASM

Nature of the Sky WASM is a WebAssembly Binary sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.

04-nature-sky.wasm

Type Sample

Small file

327 B

Wikimedia Commons CC0 1.0

SHA-256 3ada2eabf427fc9fc21cf1713a821a1d1e4193d74b624b8b7321078f22918a9f

Download

Exe

Sky Landscape WASM

Sky Landscape WASM is a WebAssembly Binary sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.

05-sky-landscape.wasm

Type Sample

Small file

425 B

Wikimedia Commons Public domain

SHA-256 2dbb097173a291c69ba274c3b7657578487c7ffdc7e9d46d3b74215b2a0876ee

Download

Exe

Starry Sky WASM

Starry Sky WASM is a WebAssembly Binary sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.

06-starry-sky.wasm

Type Sample

Small file

331 B

Wikimedia Commons Public domain

SHA-256 0ed0619787a21029e139ff45f99b80f31374eab5dc8f1ffccaf9b2f187829e4e

Download

Exe

Blue Night Sky WASM

Blue Night Sky WASM is a WebAssembly Binary sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.

07-blue-night-sky.wasm

Type Sample

Small file

423 B

Wikimedia Commons CC0 1.0

SHA-256 2e6576e9a84e7ced5e8481ac7a3f065023aff2a67991a39364bbbf64f01273ea

Download

Exe

Hibiscus Flower WASM

Hibiscus Flower WASM is a WebAssembly Binary sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.

08-hibiscus-flower.wasm

Type Sample

Small file

592 B

Wikimedia Commons CC0 1.0

SHA-256 7b55237415e60f07e1385274ba7ab0e43f39126351d1440626a8c00f3766477f

Download

Exe

Arctic Sky WASM

Arctic Sky WASM is a WebAssembly Binary sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.

09-arctic-sky.wasm

Type Sample

Small file

498 B

Wikimedia Commons CC0 1.0

SHA-256 bce4c5240caa389f39154830232787b121e0500c9ffea6da63b55354a17e7f18

Download

Exe

NASA Blue Marble WASM

NASA Blue Marble WASM is a WebAssembly Binary sample based on NASA Image and Video Library. It can be used to test downloads, parsers, previews, and file type detection.

nasa-blue-marble-2012-east.wasm

Type Sample

1.0 KB

NASA Image and Video Library NASA media usage guidelines

SHA-256 97fd8605fa0f628a25a17081d28123f0d20716d3fb568de0e7cadc854ece9887

Download

Frequently asked questions

What is the magic number (file signature) of WebAssembly Binary?

WebAssembly Binary files begin with the byte signature 00 61 73 6D 01 00 00 00 (".asm...."). Detect the format by reading these leading bytes rather than trusting the file extension alone.

What is the MIME type of WebAssembly Binary?

The MIME type for WebAssembly Binary is application/wasm.

What file extension does WebAssembly Binary use?

WebAssembly Binary files use the .wasm extension. The extension is a convention only and does not guarantee the file contents, so combine it with signature and structure checks.

Magic numbers

Structure

Caveats

Detection example

Practical usage

Use cases

Common detection mistakes

Security notes

Using samples

Sample files

Empty WASM Module

Blue Sky WASM

Flower Garden WASM

Navy Blue Sky WASM

Nature of the Sky WASM

Sky Landscape WASM

Starry Sky WASM

Blue Night Sky WASM

Hibiscus Flower WASM

Arctic Sky WASM

NASA Blue Marble WASM

Frequently asked questions

What is the magic number (file signature) of WebAssembly Binary?

What is the MIME type of WebAssembly Binary?

What file extension does WebAssembly Binary use?

Related formats