Grammarly vs WriteHuman: Different Tools, Different Jobs
This comparison comes up a lot, and we get why — both tools touch AI-generated text, and people want to know which one will keep them from getting flagged. But Grammarly and WriteHuman are fundamentally different products trying to solve different problems.
Grammarly is a writing assistant. It's been around since 2009, and it's genuinely excellent at catching grammar mistakes, improving sentence clarity, and adjusting tone. Millions of people use it daily, and we have zero complaints about it as a grammar tool. The issue is that people assume running AI text through Grammarly will somehow make it undetectable. It won't. Grammar corrections don't address the statistical patterns that detectors like Turnitin and GPTZero actually measure.
WriteHuman, on the other hand, was built specifically for AI humanization. It takes AI-generated text and attempts to rewrite it so detectors can't flag it. That's the right idea — it's just that the execution falls short of what most users need. A 65% bypass rate sounds decent until you realize it means your text still gets caught about one in three times. If you're submitting a university essay or publishing content for a client who runs detection scans, those odds aren't comfortable.
AI Detection Bypass: The Numbers
We ran a head-to-head test in January 2026. We took 300 ChatGPT-generated essays (mixed topics, mixed lengths, all GPT-4o) and processed each through three pipelines: Grammarly with all suggestions accepted, WriteHuman on its default settings, and SupWriter on Standard mode. Then we submitted every output to Turnitin, GPTZero, and Originality.ai.
Grammarly results: 48% overall bypass rate. Turnitin flagged 58% of texts, GPTZero flagged 54%, Originality.ai flagged 46%. The grammar improvements are real — the text reads better — but the AI detection scores barely moved from the raw ChatGPT baseline. Grammarly's corrections operate on a different layer than what detectors scan for.
WriteHuman results: 65% overall bypass rate. Noticeably better than Grammarly, which makes sense since WriteHuman is actually designed for this. Turnitin flagged 39%, GPTZero flagged 33%, Originality.ai flagged 29%. The problem? Consistency. Some essays passed easily, others got flagged hard. WriteHuman seems to struggle with longer-form content and technical topics where the AI patterns are more pronounced.
SupWriter results: 99.2% overall bypass rate. Turnitin flagged 0.7%, GPTZero flagged 0.8%, Originality.ai flagged 1.1%. The handful of texts that didn't pass were edge cases involving highly formulaic content (legal boilerplate, mostly). For typical essays, articles, and blog posts, the bypass was effectively 100%.
We're not trying to trash WriteHuman here — 65% is better than most tools we've tested, and it's leagues ahead of Grammarly for this specific use case. But there's a meaningful difference between “works most of the time” and “works reliably enough to stake your grade on.”
When to Use Each Tool
Use Grammarly when: you're writing your own text (not AI-generated) and want grammar, clarity, and tone improvements. Grammarly is still the best in class for this. It's also great as a final polish step after humanization. If you're weighing it against other grammar tools, our Grammarly vs QuillBot comparison breaks down those differences.
Use WriteHuman when: you need a quick humanization pass on short-form content and a 65% bypass rate is acceptable for your use case. It works okay for low-stakes content like social media posts or internal drafts that might get casually scanned but aren't going through rigorous detection. Curious how it compares to other humanizers? See our QuillBot vs WriteHuman breakdown.
Use SupWriter when: the stakes matter. University submissions scanned by Turnitin. Client articles checked by Originality.ai. SEO content where you can't afford to get flagged. Anything where a 35% failure rate (WriteHuman) or a 52% failure rate (Grammarly) would cause real problems. That's where the 99%+ bypass rate earns its keep.
Why SupWriter Outperforms Both for AI Humanization
The technical difference comes down to what each tool changes in the text. Grammarly makes surface corrections — comma placement, word choice, sentence clarity. These are valuable edits, but they don't touch the statistical fingerprint AI detectors measure.
WriteHuman goes deeper, using synonym replacement and sentence restructuring to shake up the text. That's enough to fool simpler detectors, but the more sophisticated ones (Turnitin's latest model, Originality.ai v3) still pick up on residual patterns. The perplexity profile might shift, but the overall distribution often stays within the range detectors flag as AI.
SupWriter takes a fundamentally different approach. Instead of editing on top of AI patterns, we decompose the text and rebuild it with human-like variation baked in at the structural level. Sentence length variation, unpredictable word choices, deliberate asymmetries in paragraph flow — the kind of “messiness” that characterizes real human writing. The meaning stays intact. The AI fingerprint doesn't.
We also include a built-in AI detector with 99% accuracy so you can verify your text passes before submitting. Grammarly's detector has a 34% false positive rate — it flags genuine human writing as AI a third of the time. WriteHuman doesn't include a detector at all, so you're flying blind.
And then there's pricing. SupWriter starts at $9.99/month. Both Grammarly Premium and WriteHuman charge $12/month. You're paying less for a tool that performs measurably better on the metric that actually matters — getting past AI detectors without sacrificing the quality of your content.
Related Resources
- Grammarly vs QuillBot — The most popular comparison
- QuillBot vs WriteHuman — Paraphraser vs humanizer
- Best Grammarly Alternative — For AI humanization
- Does Grammarly Detect AI? — Our test results
- Best AI Humanizer Tools — Complete ranked list