What Grammarly's AI detection does
Grammarly's AI detection is a binary classifier that flags text as likely AI-generated or human-written. It is built into the Grammarly editor and runs alongside grammar, clarity, and tone suggestions. The feature is available on Business and Enterprise plans; it is not available on free accounts.
When AI content is detected, Grammarly shows a banner or sidebar indicator with a percentage estimate of AI-generated content. It does not show which parts of the text triggered the detection or which signals contributed to the score.
How accurate is it?
Grammarly has not published independent benchmark results for its AI detection feature. Based on user testing and independent comparisons:
Obvious, unedited GPT output
Generally caughtDirect ChatGPT or Claude output submitted without changes is detected with reasonable reliability. Most users report consistent flags in this category.
Lightly edited AI output
InconsistentPerformance degrades noticeably when AI text has been lightly revised. Users report significant variation, with some edited AI content passing without a flag.
Paraphrased AI content
Frequently missesSingle-model detectors without semantic models perform poorly on paraphrased content. There is no published evidence that Grammarly's detector uses a semantic model layer.
Formal human writing
False positives reportedAcademic writing, legal prose, and formal business writing from human authors trigger false positives at an uncharacterized rate. Grammarly has acknowledged this limitation.
The core problem: it is a grammar tool, not a detector
Grammarly was built to improve writing. AI detection was added as a feature in response to market demand, not as a core engineering focus. The implications of this:
Single model, no ensemble
Dedicated AI detectors run multiple independent models and combine their outputs. Grammarly runs one classifier. A single model has predictable failure modes: it is optimized against the content it was trained on and degrades on content types, model outputs, and editing patterns it has not seen.
No explainability
Grammarly shows a percentage but not which signals drove the score. When you get a 73% AI flag, you have no way to know whether the statistical pattern was sentence structure, word choice, phrase patterns, or coherence. Without knowing what triggered the score, you cannot address it.
Optimized for editing, not detection
The underlying architecture is designed to make grammar corrections and clarity suggestions. The same processing pipeline is repurposed for AI detection. Dedicated detectors build their architecture around detection from the ground up, allowing for more specialized feature extraction.
No independent benchmarking
GPTZero, Originality.ai, and Airno have all published or participated in independent accuracy comparisons. Grammarly has not. Without third-party benchmarks, the 99% accuracy claims in their marketing are not verifiable.
Grammarly vs dedicated AI detectors
When Grammarly's detection is sufficient
Grammarly's AI detection is not a bad tool for what it is. It is reasonable for:
- •A quick first-pass check on content you are already editing in Grammarly, where you do not want to copy text to a separate tool
- •Low-stakes checks where a rough signal is enough and you do not need to know which signals fired
- •Teams already on Grammarly Business who want detection without adding a separate tool subscription
It is not sufficient for high-stakes decisions, educational integrity cases, publishing workflows that require explainability, or any situation where you need to know why a score is high (not just that it is). In those cases, use a dedicated detection tool with multiple independent signals and a per-detector breakdown.
Can you write with Grammarly and not be flagged?
Using Grammarly's grammar and style suggestions on human-written text does not make the text look more AI-generated. Grammarly suggestions are targeted edits (comma placement, passive voice, clarity), not wholesale rewrites. Running Grammarly on human writing should not increase AI detection scores in any substantive way.
The concern is the reverse: if you write text with AI, run it through Grammarly to polish it, and then resubmit, Grammarly's own detector may flag it (since it just processed the content and knows it was AI-assisted). Whether Grammarly uses its own editing history to inform its detection is not publicly documented.
Need more than a single-model flag?
Airno runs eight independent detectors and shows exactly which signals fired. Free, no Grammarly subscription needed.
Try Airno free