Matt Busche on Mythryl: “This is a great read about writing an HTML5 spec compliant parser in…”

This is a great read about writing an HTML5 spec compliant parser in Python and a fascinating follow up by Simon converting the library to JavaScript for "free" simonwillison.net/2025/Dec/15/...

simonwillison.netI ported JustHTML from Python to JavaScript with Codex CLI and GPT-5.2 in 4.5 hoursI wrote about JustHTML yesterday—Emil Stenström’s project to build a new standards compliant HTML5 parser in pure Python code using coding agents running against the comprehensive html5lib-tests testi...

Simon Willison@simonwillison.net

JustHTML by @emilstenstrom.bsky.social is a new Python library (no dependencies) that parses HTML according to the HTML5 specification and passes the 9,200 test html5lib-tests suite It's 3,000 lines of code mostly written by coding agents over a couple of months simonwillison.net/2025/Dec/14/...

simonwillison.netJustHTML is a fascinating example of vibe engineering in actionI recently came across JustHTML, a new Python library for parsing HTML released by Emil Stenström. It’s a very interesting piece of software, both as a useful library and as …

22/12/25, 4:05 pm0 reposts0 likes

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