Simon Willison’s Weblog

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Sunday, 22nd March 2026

Tool Merge State Visualizer — # CRDT Merge State Visualizer

Bram Cohen wrote about his coherent vision for the future of version control using CRDTs, illustrated by 470 lines of Python.

I fed that Python (minus comments) into Claude and asked for an explanation, then had it use Pyodide to build me an interactive UI for seeing how the algorithms work.

Tool DNS Lookup

TIL that Cloudflare's 1.1.1.1 DNS service (and 1.1.1.2 and 1.1.1.3, which block malware and malware + adult content respectively) has a CORS-enabled JSON API, so I had Claude Code build me a UI for running DNS queries against all three of those resolvers.

Research JavaScript Sandboxing Research — Analyzing current JavaScript sandboxing options for running untrusted code, this research compares core approaches in Node.js (including worker_threads, node:vm, and the Permission Model), prominent npm packages (isolated-vm, vm2), and alternative engines like quickjs-emscripten.

Aaron Harper wrote about Node.js worker threads, which inspired me to run a research task to see if they might help with running JavaScript in a sandbox. Claude Code went way beyond my initial question and produced a comparison of isolated-vm, vm2, quickjs-emscripten, QuickJS-NG, ShadowRealm, and Deno Workers.

Research PCGamer Article Performance Audit — A performance audit of the March 2026 PCGamer article on RSS readers reveals severe page bloat, with over 82% of network traffic and transferred bytes traced to ad-tech, tracking, and programmatic advertising scripts. Despite the core content consisting of just 10-15 KB of text and a handful of images (~150 KB total), the page triggers over 431 network requests and 5.5 MB of transfer (18.8 MB decoded) within 60 seconds—ballooning to 200+ MB in Firefox due to autoplay video carousels and…

Stuart Breckenridge pointed out that PC Gamer Recommends RSS Readers in a 37MB Article That Just Keeps Downloading, highlighting a truly horrifying example of web bloat that added up to 100s more MBs thanks to auto-playing video ads. I decided to have Claude Code for web use Rodney to investigate the page - prompt here.

Experimenting with Starlette 1.0 with Claude skills

Visit Experimenting with Starlette 1.0 with Claude skills

Starlette 1.0 is out! This is a really big deal. I think Starlette may be the Python framework with the most usage compared to its relatively low brand recognition because Starlette is the foundation of FastAPI, which has attracted a huge amount of buzz that seems to have overshadowed Starlette itself.

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Saturday, 21st March 2026
Monday, 23rd March 2026

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