Simon Willison’s Weblog
I'm working towards a new LLM release, and testing PRs caused me to revisit the llm-echo debug plugin. This plugin provides a "model" which doesn't involve an LLM at all - it just repeats back the prompts that have been fed to it. The new release now updates the simulated token usage counts to take tool calls, system prompts, and reasoning tokens into account.
uvx --with llm-echo llm -m echo 'hi there' -o thinking 1 --usage
First I consider the prompt, then I decide what to say. { "prompt": "hi there", "system": "", "attachments": [], "stream": true, "previous": [] } Token usage: 2 input, 24 output
Recent articles
Hello Python 3.15, goodbye 3.10, and now I can use 3.11 - 12th October 2026
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This is a beat by Simon Willison, posted on 18th October 2026 .
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