AI writing has spread so rapidly that spotting it is now a practical, everyday skill. Whether you're a teacher reviewing student essays, an editor vetting freelance submissions, or a hiring manager reading job applications, the ability to recognise AI-generated prose gives you a real advantage. The good news is that current large language models still leave clear fingerprints. Here are seven concrete signs to look for — and why each one works as a signal.
Sign 1: The Vocabulary Tell
Certain words appear in AI text at dramatically higher rates than in human writing. The landmark research paper Delving into ChatGPT usage in academic writing through excess vocabulary by Kobak et al. (Science Advances, 2025) analysed millions of PubMed abstracts and found that 74 specific words spiked in frequency after ChatGPT launched in November 2022. The word "delve" alone increased by 28 times its pre-ChatGPT baseline. Other words to watch for include:
- meticulous — used casually where a human would say "careful"
- nuanced — deployed to signal sophistication without adding substance
- pivotal — ChatGPT's favourite replacement for "important"
- tapestry — almost never used by humans in non-literary contexts
- testament — as in "a testament to human ingenuity"
- comprehensive — overused as a filler adjective
- groundbreaking — applied to things that are distinctly not groundbreaking
A single word is not proof. Two or three in one document is a strong signal. Five or more is near-conclusive. Our free AI detector flags these vocabulary patterns automatically, but you can also do a quick manual search-and-count in any word processor.
Sign 2: Uniform Sentence Lengths
Human writers naturally vary sentence length dramatically. They write fragments. Then a long, meandering sentence that builds through multiple dependent clauses, digresses briefly, and finally lands on a conclusion. Then something short again. This rhythm is instinctive and almost impossible to fake consistently.
AI text — particularly from GPT-series models — defaults to what linguists call "metronomic uniformity." Most sentences fall in the 15–25 word range. Open a suspicious document, paste it into a sentence-length analyser, and a flat histogram is a red flag. Compare that to any celebrated human essayist and you'll see wild peaks and valleys.
This pattern is related to what researchers call burstiness — a statistical property of human writing that measures how clustered high-complexity sentences tend to be. Human text is bursty; AI text is not.
Sign 3: The Closing Ritual
If the final paragraph begins with "In conclusion,", "In summary,", or "To summarize," there is a very high probability the text was AI-generated. ChatGPT was trained on academic and formal writing that uses these closings, and it reproduces them reflexively.
Real human writers rarely conclude casual writing with explicit summary markers. A blog post ends with a call to action, a personal reflection, or just stops. A workplace email ends with a next step. Only formal academic writing uses these closings — and even then, student essays written by humans tend to use more varied phrasings. If you see the closing ritual in a context where it looks out of place, that incongruity is itself a signal.
Sign 4: Transition Overuse
Formal transition words — "Furthermore,", "Moreover,", "Additionally,", "Consequently,", "Nevertheless," — are the connective tissue of AI writing. ChatGPT uses them to start paragraphs at a rate far exceeding human writers. In a five-paragraph piece, having three paragraphs begin with formal transitions is unusual for a human; for ChatGPT, it is typical.
This happens because these transitions were heavily represented in the academic corpora used to train the model, and the RLHF fine-tuning process rewarded apparent coherence — which these transitions superficially provide. Human writers use these words too, but usually mid-sentence, not as paragraph openers every single time.
Sign 5: Perfectly Balanced Perspectives
Ask ChatGPT about a controversial topic and it will give equal weight to all sides. "On the one hand… on the other hand… ultimately, both perspectives have merit." This is not how humans write opinion pieces. Humans have opinions. They argue. They dismiss one side more quickly than the other. They let their biases show.
AI models are specifically trained to avoid taking positions on contested topics because taking a wrong position creates user complaints. The result is prose that sounds exhaustively fair-minded to the point of being useless. If every paragraph ends with a balanced "however" that cancels out the previous point, you are almost certainly reading AI text.
This is also detectable in factual writing: ChatGPT covers every angle comprehensively, rarely omitting any standard perspective on a topic. Human writers prioritise what they find interesting or important, which means they naturally leave things out.
Sign 6: The Absence of Specific Personal Detail
AI cannot give real examples from real life. It gives generic illustrative placeholders. Human writing says "my colleague Sarah, who runs a bakery in Hoboken" — AI writing says "a small business owner." Human writing cites "the paper I read on the train to Edinburgh in 2019" — AI writing says "recent research suggests."
This is one of the most reliable tells because it is cognitively very difficult for AI to fake. Even when prompted to add specific details, AI invents plausible-sounding but vague specifics: "a 2023 study by researchers at a leading university" rather than a real citation. Look for this pattern: does the text give you any detail you could actually verify? If every specific is just a category placeholder, it is likely AI.
Sign 7: The Enthusiasm Problem
AI writing describes everything as "groundbreaking", "innovative", "transformative", "cutting-edge", "revolutionary", "remarkable", and "unprecedented." These superlatives are deployed even for mundane subjects. A paragraph about basic spreadsheet formatting will call it a "powerful approach to data management." A sentence about taking breaks will describe it as a "transformative practice."
Human writers calibrate their enthusiasm. They save strong words for things that actually deserve them. They are also comfortable being dismissive, neutral, or bored — registers that AI avoids because they were penalised during training. If the enthusiasm level is constant and high regardless of topic, that flatness is itself unnatural.
Putting It Together: How to Use These Signs
No single sign is conclusive on its own. A human writer might use "meticulous" once; an AI piece might occasionally have a short sentence. The method is to look for clustering. If a document triggers three or more of these seven signals, the probability of AI authorship climbs steeply.
A good workflow: start with a vocabulary scan (signs 1 and 7), check the closing paragraph (sign 3), skim for transition openers (sign 4), then read the most complex argument in the piece to check for balanced both-sidesism (sign 5) and absent specifics (sign 6). This manual check takes about two minutes for a standard essay.
For a faster first screen, paste the text into our free AI detector. It automates all seven of these checks plus additional statistical analysis based on current research. If the score comes back above 70%, apply the manual checks above to confirm. If you want to understand what the score means technically, read our how it works page.
These signals apply most strongly to GPT-series models. Claude and Gemini have slightly different patterns — Claude hedges more philosophically, Gemini structures more aggressively — but all current models share the core vocabulary tells and the absence of genuine personal detail. For a comparison of AI writing styles by model, see our AI vs human writing guide, or go directly to our ChatGPT detection page for model-specific analysis.