Over the past week, a new fanworks movement has kicked off, with the aim to root out authors using generative AI. But the detection methods being implemented are questionable, and any fanfic writer could be caught in the crossfire.

Broad distaste around the use of Claude, ChatGPT, and other AI tools has long been a thing in creative communities, including the world of fanfiction. Readers and writers have passed around tips for spotting supposedly AI-generated works, citing anything from em dashes to the broad concept of purple prose. But on June 29th, an anonymous X account called @heatedrivalryai promised a seemingly more reliable solution. It posted a skin — similar to an extension — for the popular fanfic repository Archive of Our Own (AO3) that would purportedly identify coding artifacts left behind by Anthropic’s Claude bot.

“When a Claude-generated response is pasted directly into AO3 from Claude, the text is wrapped by a Claude-injected code ‘font-claude-response-body,’” said the @heatedrivalryai account. “Its presence indicates the use of Claude definitively.” When a user visits a page (like a work of fanfic) with this code, the skin turns the entire background red.

Several test posts have been published to AO3 that allow users to check if it works. The screen immediately turned red when I tested the skin against these examples myself, and I published a Claude-generated short story to run my own experiment just in case. The red screen appeared when I directly pasted from the chatbot into the editor and vanished if I pasted text (including the exact same generated story) that didn’t come straight from Claude.

The Claude detector post was accompanied by examples of fanfic where the artifacts were spotted, which the anonymous creator said was meant to demonstrate the system works, not “create an environment of mistrust or accuse particular users.” But fanfic communities have quickly mobilized to publicly name and shame writers whose published works were flagged by the tool, and its creator certainly doesn’t consider AI a positive thing. “Fandom is a uniquely connective, collaborative space. It thrives on the human element and the creative spark which drives it and feeds off it,” they said. “If we unknowingly allow AI to corrupt these spaces, what will be left of them?”

Anthropic did not respond to my request to verify if the fan-made Claude detector works as described. The methodology here does look sound, however, and our own testing backs it up. There’s no apparent reason for the Claude code to be present in a story if the bot wasn’t used somehow. But there’s a clear risk of both false negatives and overgeneralizations.

The code wrapping is only preserved if text is copied directly from Claude into AO3’s editor, so it won’t catch anything edited in Google Docs or Microsoft Word and then moved to AO3 — and as someone who writes for a living, I can testify to how risky writing straight into a CMS is. Some writers who have been flagged have already updated their works to remove the artifacts, and future works can easily evade the tool.

Conversely, the tag doesn’t reveal how heavily Claude was used in a given work. That flashbanged scarlet screen could mean the entire story was fully AI-generated, or that an author pasted a few human-written sentences into Claude for spell-checking or translation, then moved them back into AO3.

That hasn’t mattered to some fandom members, who view any use of generative AI as an inexcusable betrayal to the wider creative community. Many people cite concerns over the environmental impact of the technology and how it’s trained by scraping the open web, which likely includes fanworks uploaded to platforms like AO3.

This particular tool’s applicability is limited — AO3 isn’t the only platform for publishing fanworks, and Claude is just one of many AI models. At least one person claims they’ve written separate code that can detect “Claude, Deepseek, and some ChatGPT” usage, but they haven’t released that solution to the public or explained how it works. I asked Google and OpenAI if their models leave any traceable artifacts in text generation that could be detected by similar means, but they haven’t responded.

In fact, it’d be highly surprising if a universally reliable system existed. I’ve been reporting on the issues surrounding AI detection for a few years now, and to my knowledge, there isn’t currently a reliable technological solution for distinguishing generated text from that typed out by human hands. Systems like C2PA Content Credentials and Google’s SynthID are making some progress toward identifying generative AI in images, videos, and even audio, but these rely on invisible watermarks and metadata that don’t carry over for copy-pasted text.

That could change in the future, and AI companies have every incentive to at least solve the problem internally. Early models were trained on text indiscriminately scraped from the internet, and as human writing is crowded out by its synthetic counterpart, they could risk a “model collapse” scenario that would degrade the accuracy of outputs.

For now, though, fandom communities are still mostly relying on vibes. Most fanfics aren’t judged by a tool like the AO3 skin, but by “tells” that could include anything from specific sentence structures — like the notorious “it’s not X, it’s Y” — to overuse of flowery metaphors. (At least nobody in fandom, so far, has benches becoming men.) But we have to remember that AI often Writes Like That because it was trained on stuff that real people have written. It’s trying to replicate us. I’m not bold enough to share my own AO3 bookmarks, but I’ve definitely read some overly grandiloquent fanfics in the pre-ChatGPT internet days that wouldn’t pass this dubious sniff test.

The best solution for distinguishing AI works on AO3 is already available: the site’s robust tagging system. A “Created Using Generative AI” tag exists, and many authors do include it to disclose the use of tools like Claude. That requires honest transparency, though, and there’s little incentive for honesty given the backlash. It’s also worth remembering that fanfiction is supposed to be a hobby, not a regulated industry.

With these efforts to prevent AI from taking eyeballs away from genuine human-driven creativity, authors who don’t conform to what’s deemed to be an acceptable quality of writing may become innocent victims of the ongoing witch hunt. At least one writer has already been caught up in this because another person they trusted to edit their fic did so using Claude. So if the next fanfic you read feels a little robotic, just bear in mind that it might not actually be the product of a robot.

• Jess Weatherbed