--- title: Best Simon Willison posts — December 2025 | daily.dev description: The most upvoted Simon Willison posts from December 2025, curated by the daily.dev community. canonical: https://daily.dev/sources/simonwillison/best-of/2025/12 twitter:card: summary_large_image twitter:site: @dailydotdev og:url: https://daily.dev/sources/simonwillison/best-of/2025/12 og:type: website og:site_name: daily.dev og:title: Best Simon Willison posts — December 2025 | daily.dev og:description: The most upvoted Simon Willison posts from December 2025, curated by the daily.dev community. og:image: https://media.daily.dev/image/upload/s--VAY5ToZt--/f_auto/v1724209435/public/daily.dev%20-%20open%20graph --- # Best of Simon Willison — December 2025 1. 1 [](https://daily.dev/posts/justhtml-is-a-fascinating-example-of-vibe-engineering-in-action-wdbcf2qcq "JustHTML is a fascinating example of vibe engineering in action") Article Simon Willison · 39w JustHTML is a fascinating example of vibe engineering in action JustHTML is a pure Python HTML5 parser that passes all 9,200+ browser vendor tests and achieves 100% test coverage. The library was built over several months using AI coding agents (Claude Sonnet, Gemini Pro, Claude Opus) in VS Code, but with extensive human engineering oversight. The developer established the API design, integrated comprehensive test suites, built custom profilers and fuzzers, and made all architectural decisions while letting the AI handle code implementation. This represents "vibe engineering"—using AI agents professionally with proper code review, testing, and engineering practices—rather than "vibe coding" which produces unvetted prototypes. The project demonstrates how experienced engineers can leverage AI as a typing assistant while maintaining responsibility for design, quality, and architectural decisions. 122 9 2. 2 [](https://daily.dev/posts/your-job-is-to-deliver-code-you-have-proven-to-work-xeabx8mtw "Your job is to deliver code you have proven to work") Article Simon Willison · 38w Your job is to deliver code you have proven to work Software engineers must deliver proven, working code rather than untested contributions. This requires both manual testing (seeing the code work yourself, documenting steps, testing edge cases) and automated testing (bundling tests with changes). With AI coding agents like Claude Code, developers should train these tools to prove their changes work through testing before submission. The human developer remains accountable for ensuring code quality and providing evidence that changes function correctly. 112 12 [See all Simon Willison archives](/sources/simonwillison/best-of) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@graph":[{"@type":"CollectionPage","@id":"https://daily.dev/sources/simonwillison/best-of/2025/12#page","url":"https://daily.dev/sources/simonwillison/best-of/2025/12","name":"Best Simon Willison Posts — December 2025","description":"The most upvoted Simon Willison posts from December 2025, curated by the daily.dev community.","isPartOf":{"@type":"WebSite","url":"https://daily.dev"}},{"@type":"ItemList","@id":"https://daily.dev/sources/simonwillison/best-of/2025/12#items","numberOfItems":2,"itemListElement":[{"@type":"ListItem","position":1,"url":"https://daily.dev/posts/justhtml-is-a-fascinating-example-of-vibe-engineering-in-action-wdbcf2qcq","name":"JustHTML is a fascinating example of vibe engineering in action"},{"@type":"ListItem","position":2,"url":"https://daily.dev/posts/your-job-is-to-deliver-code-you-have-proven-to-work-xeabx8mtw","name":"Your job is to deliver code you have proven to work"}]},{"@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Sources","item":"https://daily.dev/sources"},{"@type":"ListItem","position":3,"name":"Simon Willison","item":"https://daily.dev/sources/simonwillison"},{"@type":"ListItem","position":4,"name":"Best of","item":"https://daily.dev/sources/simonwillison/best-of"},{"@type":"ListItem","position":5,"name":"December 2025"}]}]} ```