Language models leave statistical fingerprints. Their output is clean, structurally regular, and contextually hollow in ways that pattern-aware readers start to recognize on instinct. If a message has triggered that recognition, here's a systematic breakdown of the signals that confirm machine-generated text — and a triage workflow once you've identified them.
These patterns surface consistently across contexts: dating profiles, work email threads, customer support exchanges, texts from people who insist they typed every word themselves.
1. The Structure Reads Like a Template
Casual human communication doesn't arrive with an intro sentence, three supporting points, and a closing offer to help. AI-generated messages frequently do. The structural regularity that makes LLM output useful in formal writing becomes a tell in informal contexts. This is actually one of the primary features AI detectors analyze — structural predictability is a stronger signal than vocabulary alone.
2. Flawless Output, No Human Error
People typo. They write sentence fragments. They drop commas, type "teh" at 11pm, and punctuate based on cognitive load. A message that reads like it cleared a grammar checker, spell-checker, and style linter simultaneously is exhibiting default LLM behavior. The total absence of imperfection is itself a signal worth flagging.
3. The Register Doesn't Match Prior Messages
Pull up the message history with this sender. Does the formality level suddenly shift? A colleague who habitually opens with "hey quick q —" doesn't organically pivot to "I hope this message finds you well." A vocabulary or register change that doesn't track with an obvious contextual reason — a new role, a formal setting — is a reliable indicator that the author of this message isn't who you think it is.
4. It Over-Explains Unprompted
LLMs are optimized for comprehensiveness. They pre-empt objections, cover adjacent scenarios, and append an offer for further assistance. Humans answer what was asked and stop. If you sent "are you free Thursday?" and received a paragraph addressing Thursday, Friday, and "any other time that might work," that completeness wasn't organic. Unprompted exhaustiveness is a core LLM output pattern.
5. The Empathy Is Technically Present but Contextually Empty
"I completely understand how frustrating this must be" checks the warmth box without containing actual warmth. Real emotional responses reference specifics — they get the tone slightly wrong in human ways, trail off, or over-correct. When the compassionate language in a message is interchangeable with any customer service script, the model had zero knowledge of your actual situation when it generated the text.
6. No Shared Context, No Inside References
LLMs have no memory of your relationship. They can't reference what you discussed last week, use your preferred nickname, or land an in-joke that requires shared history. A message that could be sent verbatim to any recipient and still make complete sense reveals a context window that contained no personal information about you — the structural consequence of using AI to write something that should feel personal.
7. Run It Through a Detector
The most direct answer to "is this AI?" is to test the hypothesis. WriteMask's free AI detector takes any block of text and returns a probability score in seconds — no login required. One important caveat: AI detection false positives are a real problem for short texts under 100 words. On longer messages, a high-confidence score is difficult to discount.
Triage Workflow When You Suspect AI Authorship
Start with the detector. WriteMask's free AI detector gives you a concrete probability to anchor your reasoning. Then cross-reference against historical messages from that sender and check for the six structural patterns above. If the score is high and the patterns are present, asking the sender directly is usually the fastest path to resolution — most people respond honestly when the question is framed calmly rather than as an accusation.
If you're working from the other direction — using AI assistance in your own writing and concerned it reads synthetic — WriteMask achieves a 93% pass rate at making AI-written text read as human-authored. You can also benchmark your own detection instincts with the AI or Human? game. It's considerably harder than most people expect.
Originally published on WriteMask
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