Hamel Husain's three-way test finds system prompts barely steer AI writing style
HamelHusain · x · 2026-09-05
Hamel Husain and @isaacflath ran a three-way comparison on 5 writing samples: an anti-slop "writing density" prompt, a plain writing prompt, and no system prompt at all. To their surprise, the prompt mattered far less than expected in steering the output style — and they sometimes preferred the unmannered slop prompt they assumed would perform worst. They plan to run proper evals on the slop prompt next. The post also links Claude's official prompting docs, which include a dedicated Writing density section on controlling prose style.
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