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Web Assembly Decoder - Zero Extras
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wadze - WebAssembly Decoder - Zero Extras

Wadze is a library that parses WebAssembly .wasm binary files into a Python dictionary that holds the contents of the associated WebAssembly module. It does nothing more and has no dependencies. However, it is quite small, fast, can run in parallel, and could be used to build other tools that might want to manipulate WebAssembly in some way.


Here is an example showing how to use it:

import wadze

with open('input.wasm', 'rb') as file:
    data =

module = wadze.parse_module(data)

# If you also want function code decoded into instructions, do this
module['code'] = [ wadze.parse_code(c) for c in module['code']]

In this example, the resulting module is a dictionary containing the contents of the different sections of a Wasm module. For example, to see the exported objects, do this:

for exp in module['export']:

The data representation stays fairly faithful to how WebAssembly encodes modules, but wadze tries to make it a touch more "Pythonic." The final data structure is a dictionary that mostly contains a mix of lists and named tuples.

Decoding of instructions can be done in parallel using multiprocessing. For example:

import multiprocessing
pool = multiprocessing.Pool()
module['code'] =, module['code'], 100)

In informal tests on the author's machine, Wadze is able to fully decode a Wasm file containing more than 25000 functions in under 15 seconds using a single CPU core. It's even faster with multiprocessing.

Questions and Answers

Q: What's this library for?

A: The primary purpose of this library is to have a simple and efficient Wasm decoder that might be useful for building other Python tools that want to manipulate WebAssembly in some way. It might also serve an educational purpose in illustrating how WebAssembly can be easily decoded using a simple recursive descent parser.

Q: How do I install it?

A: Wadze consists of a single Python file Copy it into your project.

Q: Can I contribute?

A: Bug reports are welcome, but what you see here is what it is. Wadze is not the start of a proto-framework or an effort to make something larger. Smaller is better.


Wadze is a creation of David Beazley (@dabeaz).


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