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  "articleBody": "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).\n\nI 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:\n\n> `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`\n\n[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).\n\nI 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.\n",
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  "content_html": "<p>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 <a target=\"_blank\" rel=\"noopener noreferrer\" href=\"https://simonwillison.net/2026/Sep/27/2026-in-llms-so-far/#simon-willison-2026-in-llms.012.webp\">AI mania</a>.</p>\n<p>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:</p>\n<blockquote>\n<p><code>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</code></p>\n</blockquote>\n<p><a target=\"_blank\" rel=\"noopener noreferrer\" href=\"https://github.com/simonw/pwasm/pull/12\">42 commits later</a> (with minimal follow-up prompting) it now handles almost all of the WASM specification, and the wheel from PyPI bundles working WASM builds of <a target=\"_blank\" rel=\"noopener noreferrer\" href=\"https://micropython.org/\">MicroPython</a>, <a target=\"_blank\" rel=\"noopener noreferrer\" href=\"https://github.com/quickjs-ng/quickjs\">QuickJS</a> and <a target=\"_blank\" rel=\"noopener noreferrer\" href=\"https://github.com/bellard/mquickjs\">Micro QuickJS</a>.</p>\n<p>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.</p>\n",
  "content_markdown": "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).\n\nI 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:\n\n> `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`\n\n[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).\n\nI 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.\n",
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  "description": "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…",
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  "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",
  "tags": [
    "python",
    "vibe-coding",
    "webassembly"
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  "temporalCoverage": "2026-10-05T18:49:38.624325496+00:00",
  "title": "pwasm 0.2a0",
  "url": "https://aggr.aymericbeaumet.com/items/simonwillison-net/2026-10-01-pwasm-0-2a0/",
  "word_count": 150
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