TL;DR

A detailed set of instructions for generating an “am I being unreasonable” (AIBU) post turned up on a Mumsnet board, The Guardian reported on Wednesday 7 October. “We don’t use AI to write threads or replies on Mumsnet,” founder Justine Roberts said, tracing the text to an OpenAI-powered tool meant only to suggest thread titles.

What appeared

A member posting as AmIAComplete asked for “a sanity check” about an awkward encounter with a brother’s family, which centred on a neurodivergent relative and a child who was unwell. Instead of a human reply, the thread showed a block of instructions headed “AIBU Response Schema v.1.0”. It told an AI to deliver “a clear, forum-style ruling plus brief actionable advice”, explained Mumsnet shorthand such as ND and DD, and included guardrails such as “do not diagnose anyone”.

Members called it “really creepy” and “so disappointing”. Some pasted the prompt into a chatbot themselves and got a complete post back.

Three explanations

Mumsnet’s account changed as the thread went on. It first said the text came from a title-suggestion tool built on an OpenAI model. It then said the prompt had not come from Mumsnet at all and might have transferred from the user’s own computer. Roberts then posted in the thread herself. Mumsnet’s system does send drafts to OpenAI so it can propose a title, she confirmed, and this time what came back was instructions for an entire response. In her words, it “looks like an error on their side”.

Users were not persuaded. “We are not idiots,” one wrote, asking for a transparent explanation.

Roberts told The Guardian that nothing in Mumsnet’s systems requests, stores or uses such a prompt, and that a post-drafting tool has never even been trialled. Where the site does use AI is in software development, ad operations, analysing conversations, and alerting moderators to posts that may need attention.

Why it lands hard

Mumsnet, founded in 2000, saw monthly unique users fall 19% to 6.1 million in 2025, with 600,000 fewer posts. Its latest annual report says it is “embedding AI tools to improve productivity and enhance the user experience”, which helps explain why members were quick to suspect the worst.

Looking forward

Roberts drew two lessons: that these systems are “less predictable than the people selling them like to suggest”, and that members want Mumsnet to stay human-written. In our view, the episode is a useful warning for any UK platform that pipes user drafts to a third-party model, even for a minor feature. Members cannot see where that feature stops, so an odd output gets read as evidence of something larger, and a changing explanation makes it worse.