.wasm

What is a .wasm file?

WebAssembly is a compiled binary format for near-native browser performance — running C, C++, and Rust code directly in the browser.

Safe format
Type Code
By W3C / Mozilla / Google / Microsoft / Apple
MIME application/wasm

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What is it

You have a .wasm file — compiled WebAssembly, a binary format that runs in browsers at near-native speed. WASM lets developers run C, C++, Rust, and other compiled languages directly in a web page, enabling applications that were previously impossible in a browser: games, video editors, CAD tools, image processing, and scientific simulations.

WebAssembly was created by a W3C working group with contributors from all major browser vendors (Google, Mozilla, Microsoft, Apple). It's not meant to replace JavaScript — it's meant to complement it. JavaScript handles the UI and DOM; WASM handles the heavy computation. Figma's rendering engine, Google Earth's 3D engine, and Photoshop's web version all use WASM under the hood. The format is sandboxed by default — WASM code can't access the filesystem or network without explicit JavaScript bridges.

Every modern browser runs WASM natively — it loads alongside JavaScript with no plugins required. You don't typically write WASM directly; you compile to it from Rust (wasm-pack), C/C++ (Emscripten), or AssemblyScript (TypeScript-like). Wasmtime and Wasmer run WASM outside the browser for server-side and edge computing use cases.

Technical details
Full Name
WebAssembly Binary
MIME Type
application/wasm
Developer
W3C / Mozilla / Google / Microsoft / Apple
Magic Bytes
00 61 73 6D
Safety
.wasm is a known, safe format.
What opens it
Any modern browser (executes automatically)
FREE All
Wasmtime
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FAQ
Will WebAssembly replace JavaScript?
No. WASM and JavaScript are complementary. JavaScript handles DOM manipulation, event handling, and the web platform API. WASM handles compute-intensive tasks (image processing, physics, compression). Most WASM applications still use JavaScript for their UI layer.
What languages compile to WebAssembly?
Rust (via wasm-pack), C/C++ (via Emscripten), AssemblyScript (TypeScript-like), Go, and Zig are the most common. In theory, any language with an LLVM backend can target WASM.
Related formats