What Simon Willison thinks about coding agents
Co-creator of Django and creator of Datasette; writes daily at simonwillison.net.
Simon Willison did not write this page.
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12 dated positions, 2025 to 2026, in their own words. Our reading of what Simon Willison has said — not written or endorsed by them.
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Their wordsThese two new models, when paired with their respective coding agent harnesses, improved from “often make mistakes” to “reliable enough to use on a day-to-day basis”.
- 3 days earlier
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Their wordsThe more time I spend working with coding agents, the more convinced I am that they make software engineering even harder.
- 12 days earlier
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Their wordsFrustratingly, the actual code it ran and exact details of what it did weren’t visible to me in the ChatGPT UI. I see this lack of transparency is an anti-feature.
↗Generating running routes with GPT-6 Astra and ChatGPT Worksimonwillison.net
- 5 weeks earlier
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Their wordsI REALLY want to believe that this fixes prompt injection risks for coding agents, but I'm just not there yet
- 5 months earlier
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Their wordsit turns out you can do this if you think really hard about okay, how do I have agents prove to me that the stuff they've written works?
↗Simon Willison: Engineering practices that make coding agents work - The Pragmatic Summityoutube.com 1st of 18 in this recording
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Their wordsthe key thing about TDD is that it means that the agents won't write more than they need to.
↗Simon Willison: Engineering practices that make coding agents work - The Pragmatic Summityoutube.com 3rd of 18 in this recording
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Their wordsI think I see people who are writing code with coding agents and they're not writing any tests at all. That's a terrible idea.
↗Simon Willison: Engineering practices that make coding agents work - The Pragmatic Summityoutube.com 4th of 18 in this recording
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Their wordsone of the magic tricks about these things is that they they're incredibly consistent. If you've got a code base with a bunch of patterns in, they will follow those patterns almost to a T.
↗Simon Willison: Engineering practices that make coding agents work - The Pragmatic Summityoutube.com 8th of 18 in this recording
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Their wordsSo, I think the most important thing is sandboxing. You want your coding agent running in an environment where if something goes completely wrong, if somebody gets malicious instructions to it, that the damage is greatly limited.
↗Simon Willison: Engineering practices that make coding agents work - The Pragmatic Summityoutube.com 12th of 18 in this recording
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Their wordsI think that might be what saves us. I think the fact that no, you can't have one engineer and have him do a thousand projects because after three hours of that he's going to literally pass out in a corner.
↗Simon Willison: Engineering practices that make coding agents work - The Pragmatic Summityoutube.com 15th of 18 in this recording
- 3 months earlier
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Their wordsThe reason I think MCP may be a one-year wonder is the stratospheric growth of coding agents. It appears that the best possible tool for any situation is Bash—if your agent can run arbitrary shell commands, it can do anything that can be done by typing commands into a terminal.
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Their wordsI run in YOLO mode all the time, despite being deeply aware of the risks involved. It hasn’t burned me yet... ... and that’s the problem.