A prospect told me last week that he can tell a deck was written by AI before the third slide. I asked how. He could not explain it, which is the point. He is not running a test. He is reading, and something in his chest says "nobody wrote this".
Two years ago I wrote that AI copy sits in an uncanny valley, fluent but not felt. That was when it was still a novelty. It is not a novelty now, and the people reading your material have read thousands of the same sentences. Their detector is trained.
Here are the tells they catch. All of them are fixable in an hour with a red pen.
Adjectives with no noun behind them
"Comprehensive protection." "Robust architecture." "Seamless integration."
Each one is a claim with the evidence removed. A person writing about something they built will reach for the concrete detail, because the concrete detail is what is in their head. "It blocks the ten attack paths we saw most often last quarter" is a sentence from someone who was there.
If you delete every adjective and the sentence still says something, the adjectives were decoration. If it says nothing, you did not have a sentence.
Everything comes in threes
Three benefits. Three pillars. Three steps. Three adjectives in every list.
Threes are easy to generate and they sound finished, which is why the floor is paved with them. Real descriptions are lumpy. One thing matters much more than the others and the writer says so. When a list has exactly three items and none of them is more important than the rest, nobody chose those items.
The sentence that could belong to anyone
Swap your company name for a competitor's. Does the paragraph still work?
If yes, it was never about you. "We help organisations navigate the complexities of security" survives every substitution you can make, which is why it means nothing. This is the fastest test there is and the one most people skip.
Rhythm that never breaks
AI sentences settle into a rhythm: medium length, one clause, a comma in the middle. Ten of them in a row and the reader is asleep, even though every sentence is correct.
People write unevenly. A four-word sentence after a long one. A fragment. A line that runs on because they were mid-thought. That unevenness is not sloppiness, it is a voice, and its absence is the loudest thing in the document.
The closing line that means well
"Despite these challenges, the future looks bright." "By embracing these changes, organisations can unlock their potential."
Read the last line of your own material. If it could sit at the end of an article about a different industry without changing a word, it is not a conclusion, it is a courtesy. Cut it. End on the point.
Why this costs you deals
Your buyer is not scoring you on style. They are using your writing as evidence about how you work.
Fluent, empty copy says: nobody senior read this, nobody checked the claims, and the person who wrote it does not know the product well enough to be specific. A security buyer's whole job is deciding whether the surface matches what is underneath. Copy is the cheapest surface they have to test.
Which is unfair, because a company can have a genuinely good product and a generic website. But the buyer cannot see the product. They can see the website.
What to do instead
Write the sentence that is only true of you. The one with a number, a customer's actual words, or a limit you would rather not advertise. It will feel narrower than the version you had, and it will be the only line anyone remembers.
If a sentence would still work with three other vendors' names in it, it is not your sentence. Delete it and write yours.