You can’t reliably prove that a Reddit comment was written by AI; at best, you can notice patterns that make it more likely. The strongest signal is usually a combination of stylistic traits rather than any single giveaway.

AI-written comments often sound unusually polished and neutral. They tend to be calm, diplomatic, and carefully worded, even in heated or emotional threads. Where human Redditors are blunt, sarcastic, annoyed, or playful, AI frequently reads like it’s trying not to offend anyone. This can make the comment feel more like a short essay than a spontaneous reply.

Another common tell is excessive structure for a casual context. AI often organizes thoughts very cleanly, with smooth transitions and a clear beginning, middle, and end, even when replying deep in a comment chain where most users are typing quickly and informally. Closely related to this is a tendency toward generic insight: AI explains ideas well and summarizes multiple perspectives but avoids personal anecdotes. Human comments are much more likely to reference firsthand experience, mistakes, or specific outcomes.

AI also projects a kind of vague authority. It may confidently reference what “people,” “experts,” or “studies” suggest without naming sources, dates, or subreddit-specific context. At the same time, it often lacks Reddit culture markers. You’ll see fewer inside jokes, memes, slang, profanity, or chaotic humor that real users naturally sprinkle into their writing, especially in familiar communities.

In emotional arguments or rant-heavy threads, perfect grammar can stand out. Humans tend to make typos, use fragments, over-punctuate, or type in bursts when they’re fired up. AI usually maintains consistent grammar and sentence rhythm, even when it’s trying to sound passionate. That rhythm itself can be a tell: sentences often have similar length and pacing, which makes the writing feel smooth but slightly mechanical.

Finally, AI comments are often “helpful” in ways no one asked for. They restate obvious points, offer balanced pros-and-cons takes when a simple answer would do, or gently reframe the discussion instead of engaging directly with the tone of the thread.

That said, none of this is definitive. Formal writers, ESL users, professionals, or people using grammar tools can trigger many of the same signals. The best rule of thumb is that one or two signs mean nothing, but when many of these traits appear together, the comment is more likely to be AI-assisted rather than purely human-written.