These five failures show up in AI-generated commercial copy often enough to treat them as reliable. Each one is shown here against the same brief: a 100-word product page for a mid-range ergonomic office chair, sold direct to UK home-workers. Using one brief throughout means the before and after versions are answering the same question.
AI defaults to a house style nobody chose
Ask most current tools for product copy and they reach for the same register: upbeat, adjective-heavy, and interchangeable with copy for almost anything else being sold online. This is what a first draft typically looks like without a tone of voice steer.
Transform your home office with our ergonomic chair, designed to elevate your workday. Featuring premium materials and a sleek, modern design, this chair delivers unparalleled comfort and support. Experience the difference for yourself and take your productivity to new heights.
Given a plainer, more specific brand voice, the same facts can be written like this instead.
This chair adjusts at the seat, back and armrests, so it fits most desks and most people without extra parts to buy. The mesh back stops the material trapping heat through a full day at a laptop. If your current chair leaves your lower back sore by mid-afternoon, this one is built to stop that happening.
The tool defaults to whichever register appears most often in the copy it was trained on, which tends to be exactly this kind of generic marketing English. A useful check: strip the brand name from a draft. If the sentences would fit a competitor's chair, a different washing machine or a completely unrelated product just as well, the copy has not actually said anything about this one.
AI pads copy to hit a word count
Told to write 100 words, most tools will write close to 100 words whether or not there is enough real content to fill them. Where the product has fewer than 100 words' worth of things to say, the tool repeats the same point in different phrasing.
Sitting for long stretches can be uncomfortable, which is why we built this chair with your comfort in mind. Comfort is at the centre of everything we do, from the mesh back to the padded armrests. We know that comfort matters when you're working from home, so we designed every part of this chair around it.
The same length limit, used properly, looks like this.
Long stretches at a desk are where most chairs fail, usually at the lower back or the shoulders. This one addresses both: a mesh back that flexes with movement, and armrests that adjust independently to keep your shoulders level with the desk.
A length target is a limit. If a draft says the same thing three times with different words, cut two of the three and count what remains.
AI invents specifics that sound plausible
When a tool runs short of real detail about a product, it does not leave a gap. It produces the kind of specific claim that professional copy for this category usually contains, whether or not anything in the brief supports it.
Developed in consultation with leading physiotherapists and tested against NHS ergonomic guidelines, this chair sets a new standard in seated support.
Nothing in the brief mentions physiotherapists or NHS testing, so neither claim can be checked or stood behind. Written from what the brief actually contains, the same section reads like this.
The seat height adjusts across a wide range and the armrests move independently, so two people sharing a desk can each set it up without starting from scratch.
The tool has no way of knowing whether a physiotherapist was consulted. It generates the phrase because that pattern of words appears often in training data for products like this, and you will not always spot it, because it reads as confidently as anything else in the draft. Treat every specific claim, certification or statistic in AI output as unverified until you have checked it against the brief. If it is not in the brief, it was invented.
AI cannot hold a tone of voice across a page
Give a tool a tone of voice brief (a description of how a brand sounds in writing, covering things such as sentence length, formality and whether it uses exclamation marks) and the opening line usually matches it. By the second or third sentence, the pull back towards a default marketing register tends to reassert itself.
This chair won't shout about itself. It's built for people who spend all day at a desk and want to stop noticing their chair. And once you experience the difference, you'll wonder how you worked without it!
The brief asked for no exclamation marks and a dry, understated tone, and both slipped by the final sentence. Held consistently, the same paragraph reads like this.
This chair won't shout about itself. It's built for people who spend all day at a desk and want to stop noticing their chair. The adjustments are simple enough to make in the first five minutes and forget about after that.
A tone of voice is a set of choices held across an entire piece. When checking AI output against a tone brief, read the middle and the end closely. That is where the drift happens.
AI makes claims it cannot substantiate
Commercial copy in the UK sits under the CAP Code, the Advertising Standards Authority's rule book for non-broadcast advertising, which requires claims to be backed by evidence before they are published. AI tools have no access to a product's test data or clinical evidence, and no way of knowing whether either exists, which does not stop them producing the kind of claim that sounds like it needs both.
Clinically proven to reduce back pain and improve posture within days.
Nothing in the brief supports a clinical claim, so it has no basis and no evidence behind it if challenged. Written from what can actually be said about the product, the same point reads like this instead.
Adjustable lumbar support you can set to the curve of your own back.
The tool produces the phrase because that pattern of claim appears often in copy for this kind of product. The guide to ASA and CAP rules covers what counts as a claim needing substantiation and what does not. This is a practical summary for copywriters, not legal advice, and for a specific claim in a specific piece of copy, the CAP Code and the ASA's own guidance are the source to check.
None of this makes a tool useless for a first draft. It makes the draft something to check line by line. The guide to writing with AI without sounding like it covers how to brief and edit around these failures, and editing AI copy works through a line-by-line pass on a real draft.