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Wasm (.wasm)

.wasm file signature | application/wasm

WebAssembly (Wasm) is a portable binary instruction format for the web, standardized by the World Wide Web Consortium (W3C) and developed by the WebAssembly Community Group. It is used to run code compiled from languages such as C, C++, Rust, and AssemblyScript in web browsers, serverless environments, and other runtime platforms. As a low-level code format, it should be obtained from trusted sources, although the format itself is not inherently dangerous.

Safe

Magic Bytes

Offset 0
00 61 73 6D

Sources: Wikipedia, Neil Harvey FileSignatures

Extension

.wasm

MIME Type

application/wasm

Byte Offset

0

Risk Level

Safe

Validation Code

How to validate .wasm files in Python

Python 
def is_wasm(file_path: str) -> bool:
    """Check if file is a valid WASM by magic bytes."""
    signature = bytes([0x00, 0x61, 0x73, 0x6D])
    with open(file_path, "rb") as f:
        return f.read(4) == signature

How to validate .wasm files in Node.js

Node.js 
function isWASM(buffer: Buffer): boolean {
  const signature = Buffer.from([0x00, 0x61, 0x73, 0x6D]);
  return buffer.subarray(0, 4).equals(signature);
}

How to validate .wasm files in Go

Go 
func IsWASM(data []byte) bool {
    signature := []byte{0x00, 0x61, 0x73, 0x6D}
    if len(data) < 4 {
        return false
    }
    return bytes.Equal(data[:4], signature)
}

API Endpoint

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

See the full API documentation for all endpoints and parameters.

Related Formats

.a .com .dll .elf .exe .axf

Frequently Asked Questions

What is a .wasm file?

A .wasm file is identified by the magic bytes 00 61 73 6D at byte offset 0. WebAssembly (Wasm) is a portable binary instruction format for the web, standardized by the World Wide Web Consortium (W3C) and developed by the WebAssembly Community Group. It is used to run code compiled from languages such as C, C++, Rust, and AssemblyScript in web browsers, serverless environments, and other runtime platforms. As a low-level code format, it should be obtained from trusted sources, although the format itself is not inherently dangerous.

What are the magic bytes for .wasm files?

The magic bytes for Wasm files are 00 61 73 6D at byte offset 0. These bytes uniquely identify the file format regardless of the file extension.

How do I validate a .wasm file?

To validate a .wasm file, read the first bytes of the file and compare them against the known magic bytes (00 61 73 6D) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.

What is the MIME type for .wasm files?

The primary MIME type for .wasm files is application/wasm.

Is it safe to open .wasm files?

Wasm (.wasm) 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.