Simon Willison builds Bluesky bot checker with Opus 5.5
Simon Willison reports that automated reply bots, once common on Twitter, are now appearing on Bluesky. Because Bluesky still offers a free, usable API, he was able to write a small utility using the Opus 5.5 model that scans any Bluesky profile for signs of a reply bot. The script flags accounts that reply within seconds of other posts, never publish original content, or repeatedly answer…
Key points
- Willison created a Bluesky bot‑checker using the Opus 5.5 model.
- The script flags accounts that reply within seconds or never post original content.
- It also looks for question‑mark characters in replies as a bot signal.
The tool looks for patterns such as rapid‑reply timestamps, lack of original posts, images or links, and the presence of question‑mark characters in replies. Willison notes that the lack of a restrictive API does not stop bots, but it makes detection harder, which motivated the creation of this checker. He references recent LLM releases—Claude Opus 5.5, GPT‑6 Sol, GPT‑6 Luna—and a price‑war context, but the focus remains on the practical bot‑detection script.
Willison’s post is a personal account of building and using the checker, offering a concrete example of how current language models can be applied to platform‑specific moderation challenges.
Model page: Opus 5.5 →
Bluesky reply bot checker
Simon Willison · 27 September 2026Loading the full article…
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