Simon Willison

The more time I spend working with coding agents, the more convinced I am that they make software engineering even harder We can do amazing things with them, but unlocking their full potential requi…

@simonw·Sep 25, 2026↗

Put together some notes on Jev and the new category of system one aka decision models https://t.co/EQZvszIXQ9

@simonw·Sep 22, 2026↗

A few notes on Anthropic's new Claude Fable 5.1 - with Max thinking level I got the best SVG pelican I've had from any Anthropic model (at a hefty cost of $3.30!), which I then had it animate https:/…

@simonw·Sep 2, 2026↗

Here's my attempt at explaining what ChatGPT Work can actually do - it's a deeply confusing but extremely powerful tool with a whole lot of useful features that aren't available in regular ChatGPT ht…

@simonw·Aug 31, 2026↗

What's gone wrong with AI & labor — a thought experiment A thought experiment that I think helps explain much of what’s gone wrong with AI and labor: Imagine an alternate universe in which — for wh…

@random_walker·Jul 29, 2026↗

Why Software Factories Fail: Turning the lights back on This is part two of [Why Software Factories Fail](https://x.com/dexhorthy/status/2080697380379427275) - Part 3 is here - https://x.com/dexhor…

@dexhorthy·Jul 25, 2026↗

Why Software Factories Fail or: the harness is not enough Update - the talk version of this post is live on youtube: [https://www.youtube.com/watch?v=Ib5GBkD555M](https://www.youtube.com/watch?v=Ib…

@dexhorthy·Jul 24, 2026↗

I think loops were a short-lived patch for models that couldn't reliably keep working on long problems until they hit a defined goal Fable and GPT-5.6 (and probably Kimi K3 as well) can just do that…

@simonw·Jul 23, 2026↗

I wrote about the completely wild incident where OpenAI were testing a new model and it broke out of its sandbox and broke INTO Hugging Face to steal the answers to the benchmark https://t.co/HGr5lFu…

@simonw·Jul 23, 2026↗

I interviewed @trq212 and @_catwu from the Claude Code team at @aiDotEngineer a couple of weeks ago - the video is now out, so I've published an annotated transcript of our conversation https://t.co/…

@simonw·Jul 21, 2026↗

The most interesting Fable tip I've heard so far is to let the model use its own judgement as much as possible I told it "For all coding tasks use your judgement to decide an appropriate lower power…

@simonw·Jul 3, 2026↗

After two days with Claude Fable 5 the best way I can describe it is "relentlessly proactive" - here's an example where I dropped in a screenshot of a bug and it span up custom CORS Python servers an…

@simonw·Jun 12, 2026↗

Wrote up my initial impressions of Claude Fable 5 - it has a big model smell: slow, expensive and capable of crunching through pretty much everything I threw at it https://t.co/xLybVGiR4c

@simonw·Jun 10, 2026↗

Notes on Claude Opus 4.8, plus pelicans riding bicycles for each of the five different thinking efforts https://t.co/8J0s0fLAnT https://t.co/EdJfdYIBF4

@simonw·Jun 2, 2026↗

Given the recent burst of activity around enterprise pricing and contracts, I think April 2026 was the month when both OpenAI and Anthropic found product-market fit https://t.co/0hgMfu9Khx

@simonw·Jun 2, 2026↗

I was talking with @josephruscio on the @heavybit podcast the other day when I realized that vibe coding and agentic engineering have started to blur a bit in some of my work - I published some extra…

@simonw·May 6, 2026↗

Since Anthropic publish their system prompts we can generate a diff between Claude Opus 4.6 and 4.7 - here are my notes on what's changed https://t.co/IQHuvLGmwO

@simonw·Apr 19, 2026↗

"Using coding agents well is taking every inch of my 25 years of experience as a software engineer." Simon Willison (@simonw) is one of the most prolific independent software engineers and most trus…

@lennysan·Apr 2, 2026↗

New chapter of my Agentic Engineering Patterns guide. This one is about having coding agents build custom interactive and animated explanations to help fight back against cognitive debt https://t.co/…

@simonw·Feb 28, 2026↗

Today's chapter of Agentic Engineering Patterns is some good general career advice which happens to also help when working with coding agents: Hoard things you know how to do https://t.co/sIql4OV2QR

@simonw·Feb 26, 2026↗

A few notes on the new Codex macOS Electron app - I've had a few days of preview access. I had fun poking around in the SQLite database it uses for scheduled Automations! https://t.co/0F0bvEtkde

@simonw·Feb 2, 2026↗

New TIL: running OpenClaw in Docker on my Mac - this is an officially documented path but there were still a few things that caught me out, hence my TIL https://t.co/dNYfebQqTg

@simonw·Feb 2, 2026↗

TIL on how I use Claude Code on my iPhone with GitHub Pages to preview Claude's changes while it's still working on them https://t.co/a1NRvWT4hU

@simonw·Jan 22, 2026↗

Here's a collection of useful patterns I've found after vibe-coding 150 different single-file HTML tools over the past couple of years https://t.co/CXs38rwO92 https://t.co/UuN4EfupAs

@simonw·Dec 10, 2025↗