Overview

application/wasm is the media type for WebAssembly binary modules — low-level bytecode compiled from C/C++/Rust and others that browsers execute at near-native speed. It is used for compute-intensive work like games, image processing, and cryptography.

Details

WebAssembly's strength is streaming compilation. `WebAssembly.instantiateStreaming(fetch('mod.wasm'))` downloads and compiles at the same time, before the response fully arrives. But this API works only when the response Content-Type is exactly application/wasm. If the server sends application/octet-stream or text/plain, streaming compilation is refused and it falls back to the slower path of buffering the whole ArrayBuffer before compiling.

So the MIME map of any static server or CDN serving .wasm must register application/wasm. Although wasm is already a compact binary, it is not text, so transport-layer gzip/brotli compression still applies and meaningfully reduces size.

Syntax

e.g. Content-Type: application/wasm

File extensions

Notes

• Without the exact MIME, instantiateStreaming fails with 'Incorrect response MIME type' — server configuration is critical.
• A wasm module cannot touch the DOM or network by itself and interacts only through JavaScript glue, giving it a sandbox boundary.
• If a CDN gzips .wasm, size shrinks further, but keep Content-Type as application/wasm and indicate compression via Content-Encoding.

Related types

Related headers