Monthly learnings and discoveries related to frontend, the web, and software engineering in general.

• The Claude Code source was leaked and it’s… something. You can visually explore its architecture at Claude Code Unpacked, with links to the code if you want to dig deeper. What struck me most: Claude Code is 500,000 lines of code! 🐳 You can make a good case that something much simpler would also do the trick.

• On that note, the fundamental mechanics of coding agents aren’t all that complicated. Turns out you can build your own in under 400 lines of code!

• MDN published an extensive write-up of their new frontend architecture, which they refactored from React to web components built with Lit. The most interesting part: how they got web components to render on the server—historically one of the biggest pain points. Spoiler: the solution involved Declarative Shadow DOM and a helper from Lit.

• The three pillars of JavaScript bloat explain why node_modules and JavaScript bundles are so infamously large and tangled. Shoutout also to the incredible e18e (Ecosystem Performance) project, which has been quietly making the JavaScript ecosystem better for everyone.

• What to know in JavaScript in 2026—a solid rundown of the most important new APIs and the current state of the most relevant tools and frameworks. Good catch-up read if you haven’t been following.

• Similarly: 10 new CSS and HTML APIs, most notably a new experimental API for rendering HTML inside a canvas (enabling all kinds of new visual effects), plus plenty of smaller, lesser-known additions.

• CSS scroll state queries make it easy to apply styles based on scroll state. Great for floating elements like navigation bars! Chrome-only for now, but degrades gracefully.

• What is CSS containment and how can I use it? Containment lets you give the browser hints about which elements are independent, reducing the work it needs to do during rendering and painting. It’s a bit tricky to get right, but can improve your page’s performance.

• Mise, the increasingly popular tool manager, environment manager, and task runner, now has experimental sandboxing for tasks.

• Martin Fowler on AI, how it will change software engineering, and other topics—including refactoring and the state of agile.

• Some small things I discovered this month that made my life easier:

  • Git Subtrees, a simpler alternative to submodules
  • git rebase --autostash for rebasing when the worktree has uncommitted changes
  • basename to extract a folder or file name from a full path
  • gh browse to jump from the terminal to various things on GitHub (e.g. a specific file)
  • gh run download to download artifacts from pipeline runs

Notable releases:

• VS Code Agents, a new companion app to VS Code optimized for working with multiple agents.

• Zed 0.233.5, also introducing a new UI for orchestrating agents.

• PNPM 11 Release Candidate, tightening security defaults, distancing itself further from npm, and adding pnpm sbom for vulnerability scanning.

• Next.js 16.2, addressing long-standing vendor lock-in concerns with a new Adapters API that makes deploying to platforms other than Vercel more straightforward.

• Git 2.54, adding a new history command for editing commit messages and splitting commits without rebasing, plus a configuration-based format for hooks.

• Claude Opus 4.7, iterating on its predecessor’s strengths—notably tool use and image recognition—though it’s drawn criticism for excessive token use and higher cost.

• Claude Code Desktop, with a redesigned UI.