AI copy sounds like AI because of what it leaves out: no prices, no names, no awkward detail, no opinion. ChatGPT prompts for copywriting do not fix that with a better instruction to sound human. They fix it by making specificity a requirement, banning the phrases that give the draft away, and forcing every sentence to carry information you supplied.
Nothing here detects whether a text was written by a machine. There is no reliable test, and pretending otherwise wastes an afternoon. What follows is a working method: build a voice profile from your own writing, rewrite against it, then apply an editing pass that removes anything a stranger could have written about any company.
What actually makes copy sound machine-written
The tells are not vocabulary. They are structure and vagueness.
- Adjective stacking: "fast, reliable, and affordable" describes nothing.
- Symmetrical lists of three: three benefits, three features, three adjectives, always in the same rhythm.
- Sentence shapes that repeat: subject, verb, long clause, period, again.
- Absence of numbers: no price, no time, no size, no date, no place.
- Announcing the message: lines that restate the heading in a longer form.
- Sympathetic vagueness: "we understand you have been through a lot" written by someone who does not know you.
- Frictionless endings: a summary paragraph that repeats what was already said.
One of these is fine. Six of them in a short email is what makes a reader stop reading.
Four constraints that fix most of it
Give every prompt these four and the drafts improve immediately.
- Specificity requirement. "Every claim must contain a number, a name, a place, a date, or a concrete object. If a sentence has none, cut it or ask me for the fact."
- Banned phrase list. Name the words and shapes you never write. A model will not guess your list.
- Length ceiling. "Under [word count] words." Models pad when given open space.
- One idea per sentence. "No sentence may carry two claims."
Also state the reader and the action once, at the top. Copy aimed at everyone converts for no one.
Copy-ready prompt: build a voice profile from your writing
I run [business or practice] and I write my own copy. Below are four samples of my writing: [paste samples]. Analyse them and produce a voice profile I can paste into future prompts. Cover: average sentence length and how much it varies, first person or second person, how I open, how I close, punctuation habits, whether I use contractions, which words I use often, and which I never use. Quote a line from each sample as evidence for every claim. Do not invent traits I have not shown, and do not give me generic marketing advice dressed as my voice.
Fill in these details
- Four samples, not one: A single email will make the profile match that email's occasion.
- Real writing only: Pasted sales pages and emails, not a company bio.
- Include rough samples: If your real writing is plain, a profile that adds flourish will undo your advantage.
The evidence quotes matter. If the profile claims you never open with a rhetorical question and your own samples do, you have caught the model inventing a persona, which it does often.
The rewrite prompt that removes the machine voice
Rewrite the copy below so it reads like one specific person wrote it to one specific reader. Constraints: every claim contains a number, a name, a place, a date, or a concrete object; no sentence carries two claims; total length under [word count] words; cut every adjective that does not change what the reader would do. Use this voice profile: [paste profile]. Banned: [your list, for example: one-stop shop, next level, effortlessly, dream bigger, world-class]. Do not add claims, numbers, offers, or credentials I have not given you. If a sentence needs a fact I have not supplied, leave a bracket like [NEED NUMBER] rather than inventing it. Original copy: [paste]
Run this twice. The first pass fixes the tells. The second pass, read against the original, is where you catch what the rewrite quietly removed.
Worked example: the same email, before and after
Before, from a plausible first draft:
Dear Valued Customer, We are delighted to introduce our innovative new laundry service, a fast, reliable, and affordable solution designed to modern households. Our team works hard to deliver outstanding quality. Book now to experience the difference.
After, using the same facts plus the missing ones:
Your shirts come back creased because the dryer runs hot for everyone. Ours runs the cotton cycle for anything under 40 degrees. Wash and fold, collected Tuesday, returned Thursday, £14 a kilo. Same-day if you drop before 9. Want the Tuesday slot? Reply with your street and we will send the bag.
The second version is shorter and less impressive-sounding. It is also the one a reader can act on, and every sentence in it came from a fact the business supplied. That is the whole method: supply facts, forbid padding, cap the length.
Prompts for headlines, offers and calls to action
- 1. Headline from facts. "Write five headlines for [offer] using only these facts: [facts]. No question headlines, no word longer than four syllables, no colons. Each must be supportable by a fact I gave you."
- 2. Specificity injection. "Rewrite this paragraph and replace every vague phrase with a fact from my list. Where no fact exists, insert [NEED FACT]."
- 3. Offer description. "Describe [offer] in three sentences: what it is, what it costs, what the reader does next. No adjectives, no benefit stacking."
- 4. Call to action test. "Here is my call to action: [paste]. Write five alternatives that ask for one specific action, and mark which one asks for the least commitment."
- 5. Plain rewrite. "Rewrite this at a reading age of [age] without losing the offer or the conditions."
- 6. Cut in half. "Cut this by half. Keep every fact and the call to action. Then list what you removed and why it was padding."
- 7. Objection page. "Here are the five objections I hear: [paste]. Write one honest paragraph per objection. Do not dismiss any objection, and do not invent a policy or guarantee."
- 8. Tone limiter. "Keep my meaning exactly. Change only the tone to [plain, warm, direct]. Report any sentence where the meaning had to shift."
- 9. Proof check. "List every claim in this copy that needs evidence: a number, a name, a date, or a policy. Mark claims that look specific but have no source."
How to judge whether a rewrite worked
Read the copy with the business details covered up. If it could describe any competitor, it failed, regardless of how it reads.
Then check three specifics:
- Fact test: Every claim traceable to something you supplied.
- Shape test: No run of three symmetrical items, no repeated sentence rhythm.
- Reader test: One reader, named or clearly implied, and one action they are being asked for.
If any sentence survives all three, keep it. Most drafts lose about a third of their length in this pass, which is usually the correct result.
Common mistakes with copywriting prompt templates
- Asking for a tone instead of facts. "Sound human" is not an instruction. "Use these numbers" is.
- Empty banned list. A model cannot guess your pet peeves.
- No length cap. Unbounded length produces the padding you are trying to remove.
- Trusting invented specifics. Prices, delivery times, and guarantees get added if you leave a gap.
- Polishing in one pass. The tone pass and the fact pass fail each other. Run them separately.
Frequently asked questions
Can you tell if copy was written by AI?
Not reliably. Detectors produce false results in both directions, and confident claims about detection are not evidence. Judge the copy on specificity, structure, and fit with your voice instead.
What AI words should I ban?
The ones you would not say out loud: unlock, seamless, elevate, transform, next level, and any phrase about the modern world moving too fast. Build the list from your own rejected sentences, not from someone else's article.
Should I tell the model my brand voice in one line?
No. A voice profile built from your own written samples, quoted as evidence, works far better and is reusable across every prompt afterwards.
Does this work for long-form pages as well as ads?
Yes, at section level. Long copy fails the same way in the middle, where the facts thin out, so rewrite one section at a time against the same profile and length ceiling.
Build the profile first, then rewrite everything with it
Paste four samples of your own writing into the voice profile prompt, save the result, and run one real page through the rewrite prompt. The profile is the reusable asset here. For more tested prompts, browse the copywriting prompt collection.