Opinion: Use LLMs only for copyediting, never copy their phrasing, says author
Simon Willison shares a personal rule for working with large language models (LLMs). He argues that LLMs should act as copyeditors—handling fact‑checking, spelling, grammar and synonym suggestions—while any specific turn of phrase they propose must be rejected. The guideline, inspired by Thomas Ptacek’s approach, is meant to keep a writer’s voice authentic and avoid the “weird smell” of…
What you can do with it
AI at Work →Provides a prompt to use an LLM for fact‑checking, spelling, grammar and synonyms without copying its phrasing.
- Who for
- marketers, founders and support teams
- Cost
- free
- Effort
- minutes
Use it for
- proofread blog posts
- check factual accuracy
- find alternative wording
Watch out Requires strict discipline to avoid using any LLM‑suggested phrasing, which may limit creative expression.
Key points from the news
- Willison treats LLMs as copyeditors, not primary writers.
- He advises never using an exact phrase suggested by an LLM.
- Provides a prompt and screenshot for building a personal LLM copyediting tool.
Willison includes a screenshot of his own LLM‑based copyediting setup and publishes the prompt he uses to start building a similar tool. The prompt asks the model to flag errors and suggest alternatives but explicitly forbids the writer from adopting any exact phrasing the model returns. He positions the rule as a form of intellectual personal protective equipment, helping writers stay disciplined while still benefiting from the model’s speed and accuracy.
How To Write With An LLM
Simon Willison · 17 September 202617th September 2026 - Link Blog
How To Write With An LLM. Thomas Ptacek on using LLMs as copyeditors, not as writing assistants:
Rule Number One: You may not use a single word an LLM suggests to you.
[...] I think that as a form of intellectual personal protective equipment you should adopt the rule that any specific turn of phrase an LLM suggests is off limits. Be strict about the rule!
I won't let LLMs write content for my blog, but I use them for fact-checking, spelling and grammar and as an occasional thesaurus (see my proofreading prompt).
The rule to never use a turn of phrase suggested by an LLM feels good to me. The text has that weird smell to it, and it's also a good principle to help stay disciplined.
Later in this piece Thomas shows a screenshot of his personal LLM copyediting tool (see also this Twitter thread), and provides a prompt to help kickstart building your own.
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This text was published by Simon Willison and written by Simon Willison. It is reproduced here with attribution so you can read it in full; the rights remain with the publisher. Read it at the source ↗
Coverage and discussion
1source- Hacker News discussion · 54 pointsnews.ycombinator.com
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