Simon Willison’s Weblog

Smoke test your Django admin site. Justin Duke demonstrates a neat pattern for running simple tests against your internal Django admin site: introspect every admin route via django.urls.get_resolver() and loop through them with @pytest.mark.parametrize to check they all return a 200 HTTP status code.

This catches simple mistakes with the admin configuration that trigger exceptions that might otherwise go undetected.

I rarely write automated tests against my own admin sites and often feel guilty about it. I wrote some notes on testing it with pytest-django fixtures a few years ago.

# 3:02 pm / testing, pytest, django, python, django-admin

Introducing Command A: Max performance, minimal compute (via) New LLM release from Cohere. It's interesting to see which aspects of the model they're highlighting, as an indicator of what their commercial customers value the most (highlights mine):

Command A delivers maximum performance with minimal hardware costs when compared to leading proprietary and open-weights models, such as GPT-4o and DeepSeek-V3. For private deployments, Command A excels on business-critical agentic and multilingual tasks, while being deployable on just two GPUs, compared to other models that typically require as many as 32. [...]

With a serving footprint of just two A100s or H100s, it requires far less compute than other comparable models on the market. This is especially important for private deployments. [...]

Its 256k context length (2x most leading models) can handle much longer enterprise documents. Other key features include Cohere’s advanced retrieval-augmented generation (RAG) with verifiable citations, agentic tool use, enterprise-grade security, and strong multilingual performance.

It's open weights but very much not open source - the license is Creative Commons Attribution Non-Commercial and also requires adhering to their Acceptable Use Policy.

Cohere offer it for commercial use via "contact us" pricing or through their API. I released llm-command-r 0.3 adding support for this new model, plus their smaller and faster Command R7B (released in December) and support for structured outputs via LLM schemas.

(I found a weird bug with their schema support where schemas that end in an integer output a seemingly limitless integer - in my experiments it affected Command R and the new Command A but not Command R7B.)

# 8:37 pm / llm, structured-extraction, cohere, generative-ai, ai, llms

Anthropic API: Text editor tool (via) Anthropic released a new "tool" today for text editing. It looks similar to the tool they offered as part of their computer use beta API, and the trick they've been using for a while in both Claude Artifacts and the new Claude Code to more efficiently edit files there.

The new tool requires you to implement several commands:

• view - to view a specified file - either the whole thing or a specified range
• str_replace - execute an exact string match replacement on a file
• create - create a new file with the specified contents
• insert - insert new text after a specified line number
• undo_edit - undo the last edit made to a specific file

Providing implementations of these commands is left as an exercise for the developer.

Once implemented, you can have conversations with Claude where it knows that it can request the content of existing files, make modifications to them and create new ones.

There's quite a lot of assembly required to start using this. I tried vibe coding an implementation by dumping a copy of the documentation into Claude itself but I didn't get as far as a working program - it looks like I'd need to spend a bunch more time on that to get something to work, so my effort is currently abandoned.

This was introduced as in a post on Token-saving updates on the Anthropic API, which also included a simplification of their token caching API and a new Token-efficient tool use (beta) where sending a token-efficient-tools-2025-02-19 beta header to Claude 3.7 Sonnet can save 14-70% of the tokens needed to define tools and schemas.

# 8:53 pm / anthropic, claude, llm-tool-use, ai, llms, claude-artifacts, ai-assisted-programming, generative-ai

Xata Agent (via) Xata are a hosted PostgreSQL company who also develop the open source pgroll and pgstream schema migration tools.

Their new "Agent" tool is a system that helps monitor and optimize a PostgreSQL server using prompts to LLMs.

Any time I see a new tool like this I go hunting for the prompts. It looks like the main system prompts for orchestrating the tool live here - here's a sample:

Provide clear, concise, and accurate responses to questions. Use the provided tools to get context from the PostgreSQL database to answer questions. When asked why a query is slow, call the explainQuery tool and also take into account the table sizes. During the initial assessment use the getTablesAndInstanceInfo, getPerfromanceAndVacuumSettings, and getPostgresExtensions tools. When asked to run a playbook, use the getPlaybook tool to get the playbook contents. Then use the contents of the playbook as an action plan. Execute the plan step by step.

The really interesting thing is those playbooks, each of which is implemented as a prompt in the lib/tools/playbooks.ts file. There are six of these so far:

• SLOW_QUERIES_PLAYBOOK
• GENERAL_MONITORING_PLAYBOOK
• TUNING_PLAYBOOK
• INVESTIGATE_HIGH_CPU_USAGE_PLAYBOOK
• INVESTIGATE_HIGH_CONNECTION_COUNT_PLAYBOOK
• INVESTIGATE_LOW_MEMORY_PLAYBOOK

Here's the full text of INVESTIGATE_LOW_MEMORY_PLAYBOOK:

Objective:
To investigate and resolve low freeable memory in the PostgreSQL database.

Step 1:
Get the freeable memory metric using the tool getInstanceMetric.

Step 3:
Get the instance details and compare the freeable memory with the amount of memory available.

Step 4:
Check the logs for any indications of memory pressure or out of memory errors. If there are, make sure to report that to the user. Also this would mean that the situation is critical.

Step 4:
Check active queries. Use the tool getConnectionsGroups to get the currently active queries. If a user or application stands out for doing a lot of work, record that to indicate to the user.

Step 5:
Check the work_mem setting and shared_buffers setting. Think if it would make sense to reduce these in order to free up memory.

Step 6:
If there is no clear root cause for using memory, suggest to the user to scale up the Postgres instance. Recommend a particular instance class.

This is the first time I've seen prompts arranged in a "playbooks" pattern like this. What a weird and interesting way to write software!

# 10:27 pm / prompt-engineering, generative-ai, ai-agents, postgresql, ai, llms, llm-tool-use