Grammarly AI Checker Review: Features and Limits

Grammarly's AI checker is an option for reviewing a draft, especially if you already use its writing tools. Its output is a signal to investigate. It cannot certify that your work will satisfy an institution's detector or AI policy.

Evidence and disclosure — reviewed September 8, 2026. This is a source-based editorial review, not our own accuracy benchmark. Humanizer AI sells writing and detection tools, so we have a commercial interest in this topic.

What the checker offers

The public Grammarly checker accepts pasted text or a document upload and presents an estimated AI-text percentage. Grammarly separately documents paid AI detection inside its writing products. Availability depends on your plan and surface; see the official user guide.

This distinction matters when evaluating value. Access to a free webpage does not mean every in-editor explanation or related writing feature is free. We did not purchase a plan, test checkout, or measure the detector on a controlled corpus for this review.

How useful is the score?

A score can focus a revision conversation: which passage needs more specific evidence, clearer reasoning, or a stronger connection to your sources? It cannot answer whether your use of assistance was allowed. That depends on the relevant rules and what you actually did.

Suppose a report flags the introduction to an original essay. A useful response is to compare the introduction with your notes and assess whether it says anything concrete. Adding a genuine observation may improve the writing. Changing words solely to produce a lower score does not add evidence of authorship. This is an illustrative workflow, not a measured Grammarly output.

Accuracy claims need their test conditions

Grammarly's public page cites a RAID benchmark ranking. We have not reproduced that evaluation or tested the current product against Turnitin on matching documents. We therefore do not translate its marketing claim into an accuracy guarantee for your draft. Source: Grammarly.

Before relying on any benchmark, inspect its date, dataset, languages, models, and false-positive threshold. Determine whether it tests the same product version you will use. Edited text, mixed authorship, and the documents in your own workflow deserve separate evaluation.

AI detection, plagiarism, and writing history

These answer different questions. AI detection classifies patterns in text. Plagiarism review examines source overlap and attribution. Writing history records how a document developed. A clean result in one category does not settle the others.

For example, copied human prose may need a citation even when an AI detector finds nothing. Generated prose may have no matching source but still violate a course rule. Review citations and permitted assistance separately.

Verdict: consider Grammarly for convenient draft feedback when its documented workflow meets your needs. This review does not establish an accuracy advantage or a reason to buy solely to lower a score. Compare the institutional workflow in Turnitin vs Grammarly, or read our methodology before trying the Humanizer AI detector.