By Aryan Gupta · November 1, 2026
Most people know Grammarly as a grammar checker, but it also has an AI humanizer now. It rewrites AI writing so it sounds more natural. A ton of students already have Grammarly, so I think its humanizer is probably one of the most common ones a teacher will run into. While I was testing Optimal, I looked at a bunch of essays that went through it, and these are the things I noticed.
Compared to the other humanizers I tried, Grammarly's makes pretty light changes. It keeps most of the same ideas in the same order and mostly just rewords the sentences. That's actually why it's one of the harder ones to catch, because the result can look really close to the original AI essay.
The biggest thing I noticed was that it mixes British and American spelling. In a few of the longer essays, it changed some words to the British spelling, like "defence," "colour," and "organise," but left other words American, like "organizing" and "specialized." Normal people pretty much always stick to one or the other, so that was a big giveaway.
It also used "carry out" a lot. In one essay it said things like "carry out attacks" and "blocking is carried out" over and over.
The wording also gets kind of stiff and formal in a weird way. I saw phrases like "in terms of," "in a mental sense," and "the vagaries of the global market," which don't really sound like how a student writes.
Sometimes a sentence loses a word and stops making sense. In one essay, a sentence started with "It enables players to..." because the word "speed" got dropped, so "it" wasn't talking about anything anymore.
And underneath all of that, the essay still has the structure of an AI essay. It covers everything evenly and neatly, and there aren't any personal details or real opinions.
When the text is short, Grammarly sometimes changes so little that there's almost nothing left to notice. In my testing, the longer essays were a lot easier to catch, because its habits had more chances to show up.
Optimal checks for the mixed spelling, the repeated "carry out," and the stiff wording, and it also looks at how much the writing still reads like AI. In my tests, it caught all seven of the Grammarly essays I tried. Still, like any detector, a result should just be a reason to look closer, not proof.
You can check your own writing on Optimal for free. If you want more background, I also wrote What Is an AI Humanizer?