justhtml

I just had Codex CLI figure out where that first version ended and the new one began. It looks to me like this is the last commit before the rewrite: https://github.com/EmilStenstrom/justhtml/tree/989b70818874d... The commit after that is https://github.com/EmilStenstrom/justhtml/commit/7bab3d2 "radical: replace legacy TurboHTML tree/handler stack with new tokenizer + treebuilder scaffold" It also adds this document called html5ever_port_plan.md: https://github.com/EmilStenstrom/justhtml/blob/7bab3d22c0da0... Here's the Codex CLI transcript I used to figure this out: https://gistpreview.github.io/?53202706d137c82dce87d729263df...

JustHTML https://github.com/EmilStenstrom/justhtml is a neat new Python library - it implements a compliant HTML5 parser in ~3,000 lines of code that passes the full existing 9,200 test HTML5 conformance suite. Emil Stenström wrote it with a variety of coding agent tools over the course of a couple of months. It's a really interesting case study in using coding agents to take on a very challenging project, taking advantage of their ability to iterate against existing tests. I wrote a bit more about it here: https://simonwillison.net/2025/Dec/14/justhtml/

I just shipped a new one of these a few minutes ago (from my phone). I found out about a new Python HTML parsing library - https://github.com/EmilStenstrom/justhtml - and wanted to try it out but I'm out without my laptop. So I had Claude Code for web build me a playground interface for trying it out: https://tools.simonwillison.net/justhtml It loads the Python library using Pyodide and lets you try it out with a simple HTML UI. The prompts I used are in this PR: https://github.com/simonw/tools/pull/156