---
title: pwasm 0.2a0
link: https://simonwillison.net/2026/Oct/1/pwasm/
source: simonwillison-net
published: 2026-10-01T17:10:31Z
updated: 2026-10-01T17:10:31Z
first_seen: 2026-10-05T18:49:38.624325496Z
labels:
- python
- vibe-coding
- webassembly
summary: 'Release: pwasm 0.2a0 pwasm is one of my folly projects - an entirely vibe-coded pure Python WebAssembly engine that I built in January during my first bout of AI mania. I hadn''t touched it since January, so I decided to let Claude Opus 5.5 loose on it and see if it could make any significant improvements: Evaluate current state of pwasm - then consider what it would take to get the MicroPython and micro JavaScript experiments from the research repo working under it - and what it would take to speed it up 42 commits later (with minimal follow-up prompting) it now handles almost all of the WASM specification, and the wheel from PyPI bundles working WASM builds of MicroPython, QuickJS and Micro QuickJS. I wouldn''t trust this thing at all - hence the alpha version tag - but it''s interesting seeing how today''s models can improve on the work of models from 10 months ago. Tags: python, webassembly, vibe-coding'
content: extracted
html: 2026-10-01-pwasm-0-2a0.html
---

pwasm is one of my folly projects - an entirely vibe-coded pure Python WebAssembly engine that I built in January during my first bout of [AI mania](https://simonwillison.net/2026/Sep/27/2026-in-llms-so-far/#simon-willison-2026-in-llms.012.webp).

I hadn't touched it since January, so I decided to let Claude Opus 5.5 loose on it and see if it could make any significant improvements:

> `Evaluate current state of pwasm - then consider what it would take to get the MicroPython and micro JavaScript experiments from the research repo working under it - and what it would take to speed it up`

[42 commits later](https://github.com/simonw/pwasm/pull/12) (with minimal follow-up prompting) it now handles almost all of the WASM specification, and the wheel from PyPI bundles working WASM builds of [MicroPython](https://micropython.org/), [QuickJS](https://github.com/quickjs-ng/quickjs) and [Micro QuickJS](https://github.com/bellard/mquickjs).

I wouldn't trust this thing at all - hence the alpha version tag - but it's interesting seeing how today's models can improve on the work of models from 10 months ago.