Simon Willison
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simon.fedi.simonwillison.net.ap.brid.gy
Simon Willison
@simon.fedi.simonwillison.net.ap.brid.gy
9.2K followers 3 following 1.4K posts
Open source developer building tools to help journalists, archivists, librarians and others analyze, explore and publish their data. https://datasette.io […]

[bridged from https://fedi.simonwillison.net/@simon on the fediverse by https://fed.brid.gy/ ]
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simon.fedi.simonwillison.net.ap.brid.gy
If you've been following my blog you'll have seen all of this already - I send out the newsletter by copy-pasting in my blog content since the last newsletter using a custom tool I built in an Observable notebook https://simonwillison.net/2023/Apr/4/substack-observable/
Semi-automating a Substack newsletter with an Observable notebook
I recently started sending out a weekly-ish email newsletter consisting of content from my blog. I’ve mostly automated that, using an Observable Notebook to generate the HTML. Here’s how that …
simonwillison.net
November 11, 2025 at 4:40 PM
simon.fedi.simonwillison.net.ap.brid.gy
I ran their "Write a POV-Ray file that shows a pelican riding on a bicycle" prompt against the new gpt-5-codex-mini and got the worst result yet! https://simonwillison.net/2025/Nov/9/pelican-on-a-bike-raytracer-edition/
Pelican on a Bike—Raytracer Edition
beetle_b ran this prompt against a bunch of recent LLMs: Write a POV-Ray file that shows a pelican riding on a bicycle. This turns out to be a harder challenge …
simonwillison.net
November 9, 2025 at 5:17 PM
simon.fedi.simonwillison.net.ap.brid.gy
For comparison, here are the pelicans riding bicycles drawn by GPT-5-Codex-Mini (the new model), GPT-5-Codex and full GPT-5 - all produced via the same hacked version of the Codex CLI tool
GPT-5-Codex-Mini. This is terrible. The pelican is an abstract collection of shapes, the bicycle is likewise very messed up GPT-5 Codex. It's a dumpy little pelican with a weird face, not particularly great but better than Mini. GPT-5: Much better bicycle, pelican is a bit line-drawing-ish but does have the necessary parts in the right places
November 9, 2025 at 3:48 AM
simon.fedi.simonwillison.net.ap.brid.gy
I also recorded a 7 minute YouTube video showing how I got Codex to reverse-engineer and then extend itself in order to draw me that pelican https://www.youtube.com/watch?v=9o1_DL9uNlM
November 9, 2025 at 3:40 AM
simon.fedi.simonwillison.net.ap.brid.gy
Since there's no API access yet I got OpenAI's Codex coding agent to rewrite itself (in Rust) to add a new "codex prompt ..." command which I could use to run prompts against the private models that are only available within that tool - full details here […]
Original post on fedi.simonwillison.net
fedi.simonwillison.net
November 9, 2025 at 3:39 AM
simon.fedi.simonwillison.net.ap.brid.gy
uv makes testing different projects against upgraded dependencies so much easier - no need to think about virtual environments, uv handles them almost invisibly

I wrote more about my uv testing tricks in this TIL https://til.simonwillison.net/python/uv-tests
Testing different Python versions with uv with-editable and uv-test
A quick uv recipe I figured out today, for running the tests for a project against multiple Python versions.
til.simonwillison.net
November 6, 2025 at 6:44 PM
simon.fedi.simonwillison.net.ap.brid.gy
And here's an example of one of my code research prompts
Create a performance benchmark and feature comparison report on PyPI cmarkgfm compared to other popular Python markdown libraries—check all of them out from github and read the source to get an idea for features, then design and run a benchmark including generating some charts, then create a report in a new python-markdown-comparison folder (do not create a _summary.md file or edit anywhere outside of that folder). Make sure the performance chart images are directly displayed in the README.md in the folder.
November 6, 2025 at 4:06 PM
simon.fedi.simonwillison.net.ap.brid.gy
Here's my research repo - each of the 13 folders is a different research project, and the README is automatically updated by an LLM to include summaries describing each one https://github.com/simonw/research?tab=readme-ov-file#research-projects-carried-out-by-ai-tools
Screenshot of a README document with a right-side navigation panel; navigation menu shows: Filter headings search box, heading "Research projects carried out by AI tools" followed by project list: sqlite-query-linter (2025-11-04), h3-library-benchmark (2025-11-04), h3o-python (2025-11-03), wazero-python-claude (2025-11-02), datasette-plugin-skill (2025-10-24), blog-tags-scikit-learn (2025-10-24), cmarkgfm-in-pyodide (2025-10-22), python-markdown-comparison (2025-10-22), datasette-plugin-alpha-versions (2025-10-20), deepseck-ocr-nvidia-spark (2025-10-20), sqlite-permissions-poc (2025-10-20), minijinja-vs-jinja2 (2025-10-19), node-pyodide (2025-10-19)
November 6, 2025 at 4:03 PM
simon.fedi.simonwillison.net.ap.brid.gy
It's a great TikTok! https://www.tiktok.com/@belligerentbarbies/video/7568380008633257271
November 5, 2025 at 3:24 PM
simon.fedi.simonwillison.net.ap.brid.gy
And in case you don't make it as far as the "miscellaneous tips" section, here's a bunch of lessons I learned about working with coding agents that I picked up along the way https://simonwillison.net/2025/Nov/4/datasette-10a20/#miscellaneous-tips-i-picked-up-along-the-way
When working on anything relating to plugins it’s vital to have at least a few real plugins that you upgrade in lock-step with the core changes. The tadd and radd shortcuts were invaluable for productively working on those plugins while I made changes to core. Coding agents make experiments much cheaper. I threw away so much code on the way to the final implementation, which was psychologically easier because the cost to create that code in the first place was so low. Tests, tests, tests. This project would have been impossible without that existing test suite. The additional tests we built along the way give me confidence that the new system is as robust as I need it to be. Claude writes good commit messages now! I finally gave in and let it write these—previously I’ve been determined to write them myself. It’s a big time saver to be able to say “write a tasteful commit message for these changes”. Claude is also great at breaking up changes into smaller commits. It can also productively rewrite history to make it easier to follow, especially useful if you’re still working in a branch. A really great way to review Claude’s changes is with the GitHub PR interface. You can attach comments to individual lines of code and then later prompt Claude like this: Use gh CLI to fetch comments on URL-to-PR and make the requested changes. This is a very quick way to apply little nitpick changes—rename this function, refactor this repeated code, add types here etc. The code I write with LLMs is higher quality code. I usually find myself making constant trade-offs while coding: this function would be neater if I extracted this helper, it would be nice to have inline documentation here, this changing this would be good but would break a dozen tests... for each of those I have to determine if the additional time is worth the benefit. Claude can apply changes so much faster than me that these calculations have changed—almost any improvement is worth applying, no matter how trivial, because the time cost is so low. Internal tools are cheap now. The new debugging interfaces were mostly written by Claude and are significantly nicer to use and look at than the hacky versions I would have knocked out myself, if I had even taken the extra time to build them. That trick with a Markdown file full of upgrade instructions works astonishingly well—it’s the same basic idea as Claude Skills. I maintain over 100 Datasette plugins now and I expect I’ll be automating all sorts of minor upgrades in the future using this technique.
November 4, 2025 at 9:47 PM