Grammarly AI Detector Review: Does World's Most Popular Writing Assistant Know What AI Looks Like?

Grammarly is the go-to for millions of writers—but it just entered the controversial game of AI detection. Does the world's most popular writing assistant really know what AI looks like?

Promises vs. Reality

Grammarly says its AI detector can identify text written by popular LLMs and claims not to just focus on "writing style" and "fluency."

What We Observed

#1. The Grammarly Trap That May Bite Grammarly

One interesting irony we found: When people use Grammarly's AI suggestions for grammar and clarity, they seem more likely to be flagged by its detector. Writing often looks suspiciously uniform when AI suggestions dictate how to make every line "better."

#2. Sensitivity Settings

Grammarly's detector seems to err on the side of caution a little more than GPTZero and Originality, but false positive problems are still rampant (we're seeing a 10% False Positive Rate (FPR) in our internal tests). See Why AI Detectors Fail for more on false positives.

How to Pass

It takes returning to real human variation in sentence structures to pass the test with flying colors—something those "helpful clarity suggestions" tend to remove completely. This is exactly how RewriteAI's humanizer works. See our Best AI Humanizer guide for a full comparison.