dewasm converts WebAssembly binaries into pure source code for languages like Ruby, Bash, and Go. No WebAssembly runtime is required.

Here is cowsay, a WebAssembly binary, converted to a pure Bash script and run with nothing but bash:

$ dewasm examples/apps/cache/cowsay.wasm --target bash --mode standalone -o cowsay.sh
$ echo "Hello from Bash" | bash cowsay.sh
 _________________
< Hello from Bash >
 -----------------
        \   ^__^
         \  (oo)\_______
            (__)\       )\/\
               ||----w |
                ||     ||

As a larger example, QuickJS-NG, a JavaScript engine written in C, can be converted just as well, this time to pure Ruby:

$ dewasm examples/apps/cache/qjs.wasm --target ruby --mode standalone -o qjs.rb
$ ruby qjs.rb -e 'console.log("2**16 =", 2**16); console.log(JSON.stringify(["Ruby", "JavaScript"].sort()))'
2**16 = 65536
["JavaScript","Ruby"]

A WebAssembly binary can also be used as a library instead of a standalone application. Here, a small example add.wat is converted and its add export is called directly from Ruby:

$ dewasm examples/wat/add.wat --target ruby --mode library --module-name Add -o add.rb

require_relative "add"

inst = Add.new
inst.invoke("add", 2, 3) # => 5

Beyond simple examples, dewasm scales to real libraries and applications too:

• examples/rails demonstrates that SQLite, converted to pure Ruby by dewasm, can be used as the database engine for a Rails app.
• examples/doom shows how dewasm can port the WebAssembly version of DOOM to multiple programming languages, including Bash.
• examples/nes converts a NES emulator (agnes) once and turns every backend language into a native NES player — the ROM is a file you pass in, not part of the artifact.

Here is a quick summary of what dewasm can do:

• Support real-world binaries: Implements most of the Wasm 1.0 and WASI preview 1 specs to convert existing WebAssembly binaries.
• Target multiple languages: Translates one WebAssembly binary to several target languages, such as Ruby, Bash, and Go.
• Adapt to your needs: Generates either standalone scripts or importable library source code.
• Keep it minimal: Bundles only the specific runtime code that the WebAssembly binary actually requires.

Currently, dewasm is not published to crates.io.

$ cargo install --git https://github.com/dewasm/dewasm dewasm-cli

or:

$ git clone https://github.com/dewasm/dewasm && cd dewasm
$ cargo build --release

$ dewasm input.<wasm|wat>
    --target <ruby|bash|python|perl|go|java>
    --mode <standalone|library>
    -o output.<rb|sh|py|pl|go|java>

• input is a WebAssembly binary to be translated.
  • dewasm accepts a WebAssembly text (WAT) file too.
• --target (or -t) selects the target language (default: ruby).
• --mode (or -m) specifies the translation mode (default: library).
  • --mode standalone wires up WASI and runs the module's _start.
  • --mode library exposes the module's exports to the target language.
• --output (or -o) sets the output file (default: -).
  • When - is specified, dewasm outputs the result to stdout.
• --module-name names the generated class/package and is required in library mode (standalone output has a fixed internal name and rejects it).

Please see dewasm --help for the full list of options.

The MIT license. See the LICENSE file.

Copyright (c) 2026 Hiroya Fujinami