Simon Willison — 2026-04-13#

Highlight#

Today’s standout is Simon’s hands-on research into the newly released servo crate using Claude Code. It perfectly captures his classic approach to AI-assisted exploration, demonstrating how quickly you can prototype a Rust CLI tool and evaluate WebAssembly compatibility with an LLM sidekick.

Posts#

[Exploring the new servo crate] · Source Following the initial release of the embeddable servo browser engine on crates.io, Simon tasked Claude Code for web with exploring its capabilities. The AI successfully generated a working Rust CLI tool called servo-shot for taking web screenshots. While compiling Servo itself to WebAssembly proved unfeasible due to its heavy use of threads and SpiderMonkey dependencies, Claude instead built a playground page utilizing a WebAssembly build of the html5ever and markup5ever_rcdom crates to parse HTML fragments.

Simon Willison — 2026-04-05#

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Simon highlights a deep-dive post by Lalit Maganti on the realities of “agentic engineering” when building a robust SQLite parser. The piece beautifully articulates a crucial lesson for our space: while AI is incredible at plowing through tedious low-level implementation details, it struggles significantly with high-level design and architectural decisions where there isn’t an objectively right answer.

Posts#

Eight years of wanting, three months of building with AI Simon shares a standout piece of long-form writing by Lalit Maganti on the process of building syntaqlite, a parser and formatter for SQLite. Claude Code was instrumental in overcoming the initial hurdle of implementing 400+ tedious grammar rules, allowing Lalit to rapidly vibe-code a working prototype. However, the post cautions that relying on AI for architectural design led to deferred decisions and a confusing codebase, ultimately requiring a complete rewrite with more human-in-the-loop decision making. The core takeaway is that while AI excels at tasks with objectively checkable answers, it remains weak at subjective design and system architecture.

Simon Willison — Week of 2026-04-04 to 2026-04-10#

Highlight of the Week#

Anthropic’s decision to delay the general release of their highly capable Claude Mythos model under “Project Glasswing” marks a significant turning point in the AI industry. The move underscores a massive shift in frontier model capabilities, as models evolve from generating text to autonomously chaining multiple minor vulnerabilities into sophisticated exploits, requiring a new level of security safeguards before release.