Drop a .wasm file

Show options
Minimum size of a mapped region in bytes to be shown in the flamegraph. (WARNING: Small values can make the flamegraph very big and slow.)
Only break down to files, not functions.
Show raw object symbol names for functions, rather than demangling them.
Show DWARF debug sections in the breakdown.
🤫 Wasmphobia has experimental support for JavaScript source maps


Wasmphobia analyzes a WebAssembly file and gives you a breakdown of what contributed to the module’s size. This is only really useful when the WebAssembly binary has DWARF debugging data embedded.


You can use Wasmphobia interactively on the website or install it locally as a CLI
cargo install --git https://github.com/surma/wasmphobia

How to compile your Wasm

If you care about file size, make sure you compile your code with optimizations (like -O3 and -flto) enabled. In most languages, doing a “release” build should enable these settings for you. However, at the same time, doing a release build often strips debug information from the binary. Here’s a short list of how to do release build with debug symbols.


You can add --config "profile.release.debug=true" to your cargo invocation. If your release profile strips symbols, you will also need to disable this with --config "profile.release.strip=false". For example, to make a release build targeting WASI, you’d run:
cargo build --config "profile.release.debug=true" --config "profile.release.strip=false" --release --target wasm32-wasi

C++ / Emscripten

$(CPP) -O3 -gfull ...

Shoutouts and Credit

License Apache-2.0