Install for the Web

raylib-rs targets wasm32-unknown-emscripten, which compiles your game to WebAssembly and runs it in a browser via OpenGL ES 2 (WebGL). This path is build-verified continuously in the web.yml CI workflow.

Prerequisites

Rust 1.88+ — install via rustup.

The wasm32-unknown-emscripten target:

rustup target add wasm32-unknown-emscripten

emsdk 6.0.0+ — the Emscripten SDK provides emcc, the compiler that cross-compiles C to WebAssembly. 6.0.0+ bundles Binaryen ≥ 121, required by the wasm features rustc 1.98.0-nightly emits (older emsdk fails the link with `Unknown option ‘–enable-bulk-memory-opt’ and ‘UNREACHABLE executed at Asyncify.cpp’).

Follow the official emsdk install instructions:

git clone https://github.com/emscripten-core/emsdk.git
cd emsdk
./emsdk install 6.0.0
./emsdk activate 6.0.0
source ./emsdk_env.sh   # add emcc to PATH for this shell session

Required environment variable

The raylib-sys build script requires EMCC_CFLAGS to be set when targeting wasm32-unknown-emscripten. Set it before building:

export EMCC_CFLAGS="-v -O3 -sUSE_GLFW=3 -sASSERTIONS=1 -sWASM=1 -sASYNCIFY -sGL_ENABLE_GET_PROC_ADDRESS=1"

This exact value is used by the CI web.yml workflow.

You also need to set:

BINDGEN_EXTRA_CLANG_ARGS="--sysroot=$EMSDK/upstream/emscripten/cache/sysroot"

Bindgen uses host clang; without this it finds /usr/include/math.h (glibc) instead of the emscripten wasm sysroot, causing a fatal ‘bits/libc-header-start.h’ not found error.

See: https://github.com/raylib-rs/raylib-rs/blob/unstable/.github/workflows/web.yml#L44

Build

cargo build --target wasm32-unknown-emscripten

This compiles your project for the WebAssembly target. You can find the wasm and the js files in target/wasm32-unknown-emscripten/debug/deps.

Running in a browser

A cargo build produces a .wasm binary and a .js glue file, but running in a browser also requires an HTML shell that loads them. raylib provides an HTML shell template. The WS9 showcase site (the final workstream of the 6.0 upgrade) will provide working web examples and a reference HTML shell.

Transmission is another good example of a simple shell. Just add the js script tag at the bottom:

</script><script src=<your_project_name>.js async></script>

Known limitation

The software_renderer feature (PLATFORM=Memory / rlsw) is not currently supported on wasm32-unknown-emscripten. The software renderer is a headless desktop-testing path; WebAssembly uses WebGL (GLES2), not the CPU-only rlsw backend. This is a tracked-deferred item from WS6b; see docs/superpowers/notes/ws6b-complete.md item 5.

Known errors

If you encounter an Asyncify error such as:

UNREACHABLE executed at /b/s/w/ir/cache/builder/emscripten-releases/binaryen/src/passes/Asyncify.cpp:1142

removing -sASYNCIFY from EMCC_CFLAGS will not help. You will still get a wasm runtime error. Try switching to the latest (as of 22.06.2026) version of emsdk - 6.0.0

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