Simon Willison — 2026-05-30#

Highlight#

Today’s standout is Simon’s breakthrough in running ASGI apps entirely in the browser using Pyodide and Service Workers. Guided by Claude Opus 4.8, this research paves the way for a major architectural upgrade to Datasette Lite, solving longstanding issues with JavaScript execution and plugin compatibility that plagued the older Web Worker approach.

Posts#

Running Python ASGI apps in the browser via Pyodide + a service worker · Source Simon documents a successful experiment using Claude Opus 4.8 to transition Datasette Lite from Web Workers to Service Workers. The previous Web Worker approach intercepted navigation but unfortunately broke inline <script> tags and numerous Datasette plugins. The new service worker method successfully runs a basic ASGI FastCGI demo and Datasette 1.0a31. Simon plans to fully implement this upgrade into Datasette Lite once he completely wraps his head around the AI-generated solution.

How we contain Claude across products · Source Anthropic has released a rare, thoroughly documented overview detailing their sandboxing boundaries across Claude.ai, Claude Code, and Cowork. Simon appreciates the transparency in the sandboxing space, highlighting specific architectural boundaries like gVisor for the web platform, Seatbelt/Bubblewrap for local execution, and full VMs for Cowork. The post includes stories of exfiltration vectors they missed and prompted Simon to revisit Anthropic’s open-source srt (Anthropic Sandbox Runtime) tool for local experiments.

markdown-svg-renderer · Source A quick release of a custom Markdown rendering tool tailored for handling fenced code SVG blocks. It allows developers to seamlessly toggle via tabs between the rendered SVG image and the raw code view. The tool accepts pasted Markdown, Gists, or CORS-enabled URLs, which Simon demonstrates by loading LLM Pelican logs generated by Opus 4.8.

I Am Retiring from Tech to Live Offline · Source Simon reflects on open-source veteran Chad Whitacre’s decision to step away from the tech industry and embrace an “AI Amish” 1980s offline lifestyle. The departure was triggered by an intoxicating but deeply unsettling 12-hour side project utilizing Claude Code with Opus 4.5, which Chad described as feeling like a megacorp-owned entity was sharing his inner monologue. Simon laments the loss of Chad’s online voice, noting that generative AI’s disruption is making the already difficult open-source sustainability problem even harder to crack.

Quoting Daniel Jalkut · Source A brief link post highlighting a quote from Daniel Jalkut regarding the extreme polarization of opinions surrounding AI. Jalkut posits that everyone who is against AI is “too against it” and everyone for it is “too for it”.

Project Pulse#

The overarching theme in today’s posts is deep, hands-on collaboration with Anthropic’s latest Opus models. Simon is actively using Claude to push the boundaries of browser-based Python execution for Datasette Lite, while simultaneously digesting the broader security mechanics of Anthropic’s sandboxes and the stark, polarizing societal pushback surrounding agentic developer tools.