Leadership1 publisherNot yet confirmed elsewhere3 min readPublished
Mumsnet's shifting account of a stray AI prompt tests its human-written promise
Mumsnet gave three successive explanations for an AI prompt that surfaced in a member's advice thread, ending with its founder blaming OpenAI. Members rejected each account in turn on a forum that, in Justine Roberts's words, works because the people on it are real.
The Board Room · Leadership desk
Drafted by a language model from the sources cited here and checked against its claim ledger before publication. How we use AISend a correction
What happened
- The prompt, titled AIBU Response Schema v.1.0, appeared in reply to AmIAComplete, a member seeking advice about a neurodivergent uncle and a sick child.
- Mumsnet first denied using AI to write threads and said the prompt came from a thread-title tool that uses an OpenAI model.
- The company next said the prompt had not come from it at all and suggested it had transferred from the member's own computer.
- Founder Justine Roberts then confirmed it came from Mumsnet's own title system, a tool that sends members' drafts to OpenAI and this time returned a prompt for a whole reply.
- Roberts said Mumsnet has never tested a tool that drafts posts.
Compiled by The Board RoomSomething wrong?How this is made
Why it matters
- decision Mumsnet has to decide whether a title suggestion is worth sending members' unposted drafts to an outside model at all.
- contradiction Because the second account undid the first and the third undid the second, Roberts's final explanation inherits the doubt the earlier two created.
- precedent Members will check any future unexplained post against this episode, and expect to test the company's denials with their own AI tools before believing them.
Mumsnet's latest annual report said the company was "embedding AI tools to improve productivity and enhance the user experience" [9]. That plan serves a shrinking audience [8]. Monthly unique users fell 19% in 2025 to 6.1 million, and posts fell by 600,000 [8]. A 19% fall to 6.1 million implies about 7.5 million a year earlier, so roughly 1.4 million monthly users left [20][21]. The other side of the trade-off is the line Justine Roberts, the founder, drew in the thread: "We don't use AI to write threads or replies on Mumsnet." [3]
Roberts said the site uses AI for coding, advertising operations, conversational analysis and flagging potentially problematic posts to moderators [17]. The title tool is the one use that handles a member's words before anyone else reads them. It is also the one that failed here [13].
Members tested the first account themselves [10]. They pasted the prompt into an AI and got back a full post [10]. "We are not idiots," said one user, MrsBennetsPoorNervesAreBack. "Please can you give us a transparent explanation?" [11] When Roberts gave her explanation, users said they were being "fobbed off" [14].
The sharpest objection came from a member: "Why would OpenAI compel itself to do/try to do something so specific if it's never been asked to do that before from your side?" [15] The prompt defined house shorthand such as AIBU and DD [6]. Its rules also tracked the member's own post, telling the model "do not demean ND people; do not imply a sick child owes social performance" [7]. That detail fits either account. Roberts answered in comments to the Guardian: "nothing in our systems asks for, stores or uses anything like it" [16]. Her blame on OpenAI rests on her judgement that it "looks like an error on their side" [13]. We do not know yet how a request for a title came back as a schema for a whole reply.
If Roberts is right, part of the risk sits with a supplier. Mumsnet's promise of human-written advice would then depend in part on a model it does not operate doing only what it is asked [13]. Roberts drew a similar lesson: "these systems are less predictable than the people selling them like to suggest" [18].
Her second lesson was that "users are understandably highly concerned that Mumsnet remains written by humans" [18]. The itemised list of AI uses came in her comments to the Guardian after the thread [17]. The annual report had described the AI work in general terms [9]. I think that list, published before the error, would have given members something to check the three accounts against.
What to watch
- Whether Mumsnet keeps, changes or switches off the OpenAI-based title tool that sends members' drafts out of the site.
- Any account from OpenAI of how a request for a thread title returned a prompt for a whole reply.
- Mumsnet's next annual user and post figures, the first to cover a full year after this episode.