Simon Willison’s Weblog

• Fixed bug tracking chains of responses. Refs datasette-llm#7

This plugin works in conjunction with datasette-llm and datasette-llm-accountant to let you configure a per-user (or global) spending limit for LLM usage inside of Datasette. Configuration looks something like this:

plugins:
  datasette-llm-limits:
    limits:
      per-user-daily:
        scope: actor
        window: rolling-24h
        amount_usd: 1.00

• Tool availability can now be attached to a required_permission. The default background agent tools now require the new datasette-agent-background permission. #10

• Now uses the execute-sql permission when deciding which tables to list to the user. #8

The datasette.io site was being hammered by poorly-behaved crawlers, so I had Codex (GPT-5.5 xhigh) build a configurable rate limiting plugin to block IPs that were hammering specific areas of the site too quickly.

Here's the production configuration I'm using on that site for the new plugin:

  datasette-ip-rate-limit:
    header: Fly-Client-IP
    max_keys: 10000
    exempt_paths:
    - "/static/*"
    - "/-/turnstile*"
    rules:
    - name: demo-databases
      paths:
      - "/global-power-plants/*"
      - "/legislators/*"
      window_seconds: 60
      max_requests: 60
      block_seconds: 20

• New TokenRestrictions.abbreviated(datasette) utility method for creating "_r" dictionaries. #2695
• Table headers and column options are now visible even if a table contains zero rows. #2701
• Fixed bug with display of column actions dialog on Mobile Safari. #2708
• Fixed bug where tests could crash with a segfault due to a race condition between Datasette.close() and Database.close(). #2709

That segfault bug was gnarly. I added a mechanism to Datasette recently that would automatically close connections at the end of each test, but it turned out that introduced a race condition where an in-flight query could sometimes be executing in a thread against a connection while it was being closed. I ended up solving that by having Codex CLI (with GPT-5.5 xhigh) create a minimal Dockerfile that recreated the bug.

• Initial (silent) alpha release.

The OpenStreetMap tiles on the Datasette global-power-plants demo weren't displaying correctly. This turned out to be caused by two bugs.

The first is that the CAPTCHA I added to that site a few weeks ago was triggering for the .json fetch requests used by the map plugin, and since those weren't HTML the user was not being asked to solve them. Here's the fix.

The second was that OpenStreetMap quite reasonably block tile requests from sites that use a Referrer-Policy: no-referrer header.

Datasette does this by default, and I didn't want to change that default on people without warning - so I had Codex + GPT-5.5 build me a new plugin to help set that header to another value.

• Mechanism for configuring default options for specific models.

Part of Datasette's evolving support mechanism for plugins that use LLMs. It's now possible to configure a model with default options, e.g. to say all enrichment operations should use a specific model with temperature set to 0.5.

I was upgrading Datasette Cloud to 1.0a27 and discovered a nasty collection of accidental breakages caused by changes in that alpha. This new alpha addresses those directly:

• Fixed a compatibility bug introduced in 1.0a27 where execute_write_fn() callbacks with a parameter name other than conn were seeing errors. (#2691)
• The database.close() method now also shuts down the write connection for that database.
• New datasette.close() method for closing down all databases and resources associated with a Datasette instance. This is called automatically when the server shuts down. (#2693)
• Datasette now includes a pytest plugin which automatically calls datasette.close() on temporary instances created in function-scoped fixtures and during tests. See Automatic cleanup of Datasette instances for details. This helps avoid running out of file descriptors in plugin test suites that were written before the Database(is_temp_disk=True) feature introduced in Datasette 1.0a27. (#2692)

Most of the changes in this release were implemented using Claude Code and the newly released Claude Opus 4.7.

The datasette.io website has a news section built from this news.yaml file in the underlying GitHub repository. The YAML format looks like this:

- date: 2026-04-15
  body: |-
    [Datasette 1.0a27](https://docs.datasette.io/en/latest/changelog.html#a27-2026-04-15) changes how CSRF protection works in a way that simplifies form and API integration, and introduces a new `RenameTableEvent` for when a table is renamed by a SQL query.
- date: 2026-03-18
  body: |-
    ...

This format is a little hard to edit, so I finally had Claude build a custom preview UI to make checking for errors have slightly less friction.

I built it using standard claude.ai and Claude Artifacts, taking advantage of Claude's ability to clone GitHub repos and look at their content as part of a regular chat:

Clone https://github.com/simonw/datasette.io and look at the news.yaml file and how it is rendered on the homepage. Build an artifact I can paste that YAML into which previews what it will look like, and highlights any markdown errors or YAML errors

This plugin was using the ds_csrftoken cookie as part of a custom signed URL, which needed upgrading now that Datasette 1.0a27 no longer sets that cookie.

Two major changes in this new Datasette alpha. I covered the first of those in detail yesterday - Datasette no longer uses Django-style CSRF form tokens, instead using modern browser headers as described by Filippo Valsorda.

The second big change is that Datasette now fires a new RenameTableEvent any time a table is renamed during a SQLite transaction. This is useful because some plugins (like datasette-comments) attach additional data to table records by name, so a renamed table requires them to react in appropriate ways.

Here are the rest of the changes in the alpha:

• New actor= parameter for datasette.client methods, allowing internal requests to be made as a specific actor. This is particularly useful for writing automated tests. (#2688)
• New Database(is_temp_disk=True) option, used internally for the internal database. This helps resolve intermittent database locked errors caused by the internal database being in-memory as opposed to on-disk. (#2683) (#2684)
• The /<database>/<table>/-/upsert API (docs) now rejects rows with null primary key values. (#1936)
• Improved example in the API explorer for the /-/upsert endpoint (docs). (#1936)
• The /<database>.json endpoint now includes an "ok": true key, for consistency with other JSON API responses.
• call_with_supported_arguments() is now documented as a supported public API. (#2678)

A small update for my tool for helping me figure out what all of the Datasette instances on my laptop are up to.

• Show working directory derived from each PID
• Show the full path to each database file

Output now looks like this:

http://127.0.0.1:8007/ - v1.0a26
  Directory: /Users/simon/dev/blog
  Databases:
    simonwillisonblog: /Users/simon/dev/blog/simonwillisonblog.db
  Plugins:
    datasette-llm
    datasette-secrets
http://127.0.0.1:8001/ - v1.0a26
  Directory: /Users/simon/dev/creatures
  Databases:
    creatures: /tmp/creatures.db

• No longer requires Datasette - running uvx datasette-ports now works as well.
• Installing it as a Datasette plugin continues to provide the datasette ports command.

Another example of README-driven development, this time solving a problem that might be unique to me.

I often find myself running a bunch of different Datasette instances with different databases and different in-development plugins, spreads across dozens of different terminal windows - enough that I frequently lose them!

Now I can run this:

datasette install datasette-ports
datasette ports

And get a list of every running instance that looks something like this:

http://127.0.0.1:8333/ - v1.0a26
  Databases: data
  Plugins: datasette-enrichments, datasette-enrichments-llm, datasette-llm, datasette-secrets
http://127.0.0.1:8001/ - v1.0a26
  Databases: creatures
  Plugins: datasette-extract, datasette-llm, datasette-secrets
http://127.0.0.1:8900/ - v0.65.2
  Databases: logs

• The same model ID no longer needs to be repeated in both the default model and allowed models lists - setting it as a default model automatically adds it to the allowed models list. #6
• Improved documentation for Python API usage.

• The actor who triggers an enrichment is now passed to the llm.mode(... actor=actor) method. #3

• Now uses datasette-llm to manage model configuration, which means you can control which models are available for extraction tasks using the extract purpose and LLM model configuration. #38

• This plugin now uses datasette-llm to configure and manage models. This means it's possible to specify which models should be made available for enrichments, using the new enrichments purpose.

• Removed features relating to allowances and estimated pricing. These are now the domain of datasette-llm-accountant.
• Now depends on datasette-llm for model configuration. #3
• Full prompts and responses and tool calls can now be logged to the llm_usage_prompt_log table in the internal database if you set the new datasette-llm-usage.log_prompts plugin configuration setting.
• Redesigned the /-/llm-usage-simple-prompt page, which now requires the llm-usage-simple-prompt permission.

• The llm_prompt_context() plugin hook wrapper mechanism now tracks prompts executed within a chain as well as one-off prompts, which means it can be used to track tool call loops. #5

• Ability to configure different API keys for models based on their purpose - for example, set it up so enrichments always use gpt-5.4-mini with an API key dedicated to that purpose. #4

I released llm-echo 0.3 to provide an API key testing utility I needed for the tests for this new feature.

I'm working on integrating datasette-files into other plugins, such as datasette-extract. This necessitated a new release of the base plugin.

• owners_can_edit and owners_can_delete configuration options, plus the files-edit and files-delete actions are now scoped to a new FileResource which is a child of FileSourceResource. #18
• The file picker UI is now available as a <datasette-file-picker> Web Component. Thanks, Alex Garcia. #19
• New from datasette_files import get_file Python API for other plugins that need to access file data. #20

Adds the ability to configure which LLMs are available for which purpose, which means you can restrict the list of models that can be used with a specific plugin. #3