Simon Willison’s Weblog

Coding agents for data analysis. Here's the handout I prepared for my NICAR 2026 workshop "Coding agents for data analysis" - a three hour session aimed at data journalists demonstrating ways that tools like Claude Code and OpenAI Codex can be used to explore, analyze and clean data.

Here's the table of contents:

• Coding agents
• Warmup: ChatGPT and Claude
• Setup Claude Code and Codex
• Asking questions against a database
• Exploring data with agents
• Cleaning data: decoding neighborhood codes
• Creating visualizations with agents
• Scraping data with agents

I ran the workshop using GitHub Codespaces and OpenAI Codex, since it was easy (and inexpensive) to distribute a budget-restricted API key for Codex that attendees could use during the class. Participants ended up burning $23 of Codex tokens.

The exercises all used Python and SQLite and some of them used Datasette.

One highlight of the workshop was when we started running Datasette such that it served static content from a viz/ folder, then had Claude Code start vibe coding new interactive visualizations directly in that folder. Here's a heat map it created for my trees database using Leaflet and Leaflet.heat, source code here.

I designed the handout to also be useful for people who weren't able to attend the session in person. As is usually the case, material aimed at data journalists is equally applicable to anyone else with data to explore.

# 16th March 2026, 8:12 pm / data-journalism, geospatial, python, speaking, sqlite, ai, datasette, generative-ai, llms, github-codespaces, nicar, coding-agents, claude-code, codex-cli, leaflet

wolf-h3-viewer.glitch.me (via) Neat interactive visualization of Uber's H3 hexagonal geographical indexing mechanism.

Here's the source code.

Why does H3 use hexagons? Because Hexagons are the Bestagons:

When hexagons come together, they form three-sided joints 120 degrees apart. This, for the least material, is the most mechanically stable arrangement.

Only triangles, squares, and hexagons can tile a plane without gaps, and of those three shapes hexagons offer the best ratio of perimeter to area.

# 9th March 2025, 2:51 pm / geospatial, javascript, leaflet

tiny-world-map (via) I love this project. It’s a JavaScript file (694K uncompressed, 283KB compressed) which can be used with the Leaflet mapping library and provides a SVG base map of the world with country borders and labels for every world city with a population more than 48,000—10,000 cities total.

This means you can bundle an offline map of the world as part of any application that doesn’t need a higher level of detail. A lot of smaller island nations are missing entirely though, so this may not be right for every project.

It even includes a service worker to help implement offline mapping support, plus several variants of the map with less cities that are even smaller.

# 21st April 2024, 10:11 pm / geospatial, javascript, mapping, svg, serviceworkers, leaflet

Exploration de données avec Datasette. One of the great delights of open source development is seeing people run workshops on your project, even more so when they’re in a language other than English! Romain Clement presented this French workshop for the Python Grenoble meetup on 25th May 2023, using GitHub Codespaces as the environment. It’s pretty comprehensive, including a 300,000+ row example table which illustrates Datasette plugins such as datasette-cluster-map and datasette-leaflet-geojson.

# 27th May 2023, 12:36 am / tutorials, datasette, github-codespaces, leaflet