When we need a grammar and plagiarism checker, most of us go with the basics:
Google Docs quietly underlining things, Microsoft Word offering hit-or-miss grammar suggestions, and even your smartphone auto-corrector that tries to polish even your most casual sentences.
And to top all of that, we’re now surrounded by “advanced” AI grammar tools.
Every week, there’s a new tool popping out promising “smarter checking,” “AI-powered analysis,” and all the fancy buzzwords.
The problem with these free tools is that they cut corners.
They might miss plagiarized content or flag incorrect sentences as errors, and almost none of them can detect AI-generated content, which is kind of a big deal right now.
That brings us to PaperRater. We tested it with original content, plagiarized text, and AI-written samples to see if it catches what it should.
Read on to find out if this OG tool still has the edge to hold its own.
Key Takeaways
- PaperRater offers free grammar and plagiarism checking, but its outdated system struggles to detect copied or AI-generated content, making it unreliable for serious use.
- In testing, PaperRater accurately marked original writing as 100% unique but failed to flag fully plagiarized text, rating it 95% original despite being copied word for word.
- The tool provides readability scores and basic grammar suggestions but often flags normal words as “bad phrases” and gives inconsistent scoring feedback.
- PaperRater lacks AI detection entirely, meaning it can’t identify AI-written or AI-edited text — a major flaw in 2025, when most institutions rely on AI screening tools.
- For comprehensive writing protection, Undetectable AI remains the better choice, offering accurate AI detection, reliable plagiarism checking, and human-like rewriting through tools like the Humanizer, Paraphraser, and Stealth Writer.
What Is PaperRater?
PaperRater is a web-based tool that analyzes your writing for grammar errors, spelling mistakes, and plagiarism. It’s been around since 2007, which makes it practically ancient in internet years.
Quick Review About PaperRater
The platform markets itself as an automated proofreader and plagiarism checker. Students use it for essays.
Bloggers sometimes run drafts through it. The appeal is obvious: it’s free for basic use, and you don’t need to create an account.
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You can submit up to 5 pages at once.
The tool generates a score out of 100 based on grammar, word choice, and originality, and additionally gives you a readability grade level.
Brief Overview: PaperRater
The interface looks like it hasn’t been updated since 2015.
You paste your text into a box, select your education level (high school, college, graduate), and choose whether it’s an essay, research paper, or other document type.
Then you wait about 30 seconds while PaperRater processes everything. The results page shows your overall score, lists grammar and spelling issues, flags potential plagiarism, and gives writing suggestions.
Premium features exist, but honestly? Most people use the free version and call it a day.
How PaperRater Works
PaperRater uses automated algorithms to scan your text. It’s not checking your work against a human editor but comparing patterns against its database of grammar rules and web content.
For grammar checking, the system identifies sentence structures that typically indicate errors. Subject-verb disagreements.
Comma splices. Passive voice overuse. It marks these and suggests corrections.
The plagiarism checker compares your text against online sources. It searches for matching phrases and sentences across the web.
When it finds similarities, it flags them with a percentage match.
Here’s where it doesn’t do as well.
The tool doesn’t access paywalled academic databases like Turnitin does. It’s basically running Google searches on your sentences.
That means it misses plagiarism from printed books, subscription journals, or less-indexed websites.
The readability analysis uses standard formulas like Flesch-Kincaid.
Nothing fancy.
It counts syllables, sentence length, and word complexity to generate a grade level.
No AI detection happens. At all. PaperRater was built before ChatGPT became a thing, and they haven’t updated to include AI checking capabilities.
Testing and Results Accuracy of PaperRater
We ran two tests using the methodology inspired by ZDNet’s benchmark.
In their test, they ran both original content and copied text through multiple detection tools to see which ones actually did the job.
For reference, ZDNet ranked various AI detectors by accuracy. Undetectable AI ranked 8th in their testing.
We wrote a 120ish-word paragraph about content writing that was completely original. No copying, no AI generation. Just a person typing words.
Expected result: No plagiarism detected. Maybe a few minor grammar suggestions.
PaperRater gave the original content a 79 (C) overall. Off to a weird start. The plagiarism report came back 100 percent original, which is what you want. No matches at all. Good.
Spelling and grammar? Surprisingly, it flagged zero errors. Not even a typo. Cool.
Then it threw in a twist. PaperRater reported that our “Bad Phrase Score” was 3.78, which apparently translates to writing in the 17th percentile for the chosen education level.
It listed words like “most,” “make,” “we,” “want,” and “you” as “bad phrases.” Basically, it decided my vocabulary was too normal.
On the flip side, it loved the transitions. With a Transitional Words Score of 112, it said we did better than 95% of people. So I’m basic, but my transitions are elite. That’s balance.
Readability landed around Grade 7 to 10, depending on the formula, which aligned with general-audience writing.
Overall, the grammar and plagiarism results were accurate, but the scoring and feedback seemed random.
Test Two: Plagiarized Content
Next, we copied an excerpt directly from The New York Times word for word. Since we made no changes, it should be immediately flagged.
Expected result: High plagiarism percentage with source links.
PaperRater gave the plagiarized sample an Originality score of 95%, which is not what you want when the entire paragraph was copied word for word.
It found one matching source, flagged a tiny portion, and confidently declared the rest as “Original Work.”
In reality, none of it was original. PaperRater treated the copied text like a creative writing exercise we submitted from our hearts.
The spelling and grammar checks again found zero errors, which makes sense for published writing, but the whole point was whether it could detect plagiarism. It couldn’t.
Two major paragraphs passed as completely clean.
That’s a massive failure if you’re a teacher, editor, or student relying on this tool. It’s the exact type of false negative ZDNet warns about: when a checker misses what it should catch, you walk away feeling safe…and you shouldn’t.
PaperRater simply wasn’t able to identify most of the copied material, even when the source text was public and easily searchable.
Undetectable AI as Best Alternative
We’re not saying PaperRater is completely useless, but if you need comprehensive checking, you need better tools.
Undetectable AI provides everything you need in one platform.
You get an AI Detector that actually works, an AI Humanizer that rewrites AI-generated content to sound natural, a Paraphraser for changing sentence structures, and an AI Stealth Writer that generates content designed to bypass AI detectors from the start.
Why does this matter? Because submitting work that gets flagged as AI-written or plagiarized has real consequences. Failed assignments. Academic probation. Lost job opportunities. Damaged reputation.
PaperRater might catch basic grammar errors, but it won’t protect you from AI detection, reliably catch plagiarism, or help you rewrite problematic sections.
Undetectable AI covers all these bases. You can check your work for AI patterns, then use the Humanizer to rewrite any flagged content.
The output sounds natural because it’s designed to mimic human writing patterns, not just swap synonyms.
The Paraphraser helps you reword sources accurately, ensuring you avoid unintentional plagiarism. And the Stealth Writer creates original content that passes both AI detectors and plagiarism checkers.
It’s the difference between hoping your work is clean and knowing it is.
Can PaperRater Detect AI-Edited or Paraphrased Text?
No. Absolutely not.
PaperRater has no AI detection capabilities. If you take ChatGPT output and edit it ever so slightly, PaperRater won’t notice. If you use an AI paraphraser to rewrite content, PaperRater treats it like original work.
This is a massive downside. Employers and teachers are using AI detectors now.
Submitting AI-generated work that you think is clean because PaperRater approved it? That’s a huge risk you’re taking.
You need tools that understand AI writing patterns. PaperRater doesn’t. It’s checking for plagiarism and grammar using old-school methods that predate the AI writing boom.
AI-edited text often sounds smooth and grammatically perfect. That’s actually what makes it detectable to proper AI checkers. The patterns are too clean. The word choices are too predictable. The sentence structures are too uniform.
Undetectable AI’s Paraphraser and Stealth Writer specifically address this. They introduce natural variation, adding the subtle imperfections that make writing sound human.
They understand that real people don’t write with perfect consistency.
If you’re editing AI-generated content, you need these tools. Running it through PaperRater and getting a passing score means nothing if you later submit it to a professor using Turnitin’s AI detector or an editor using Originality.ai.
Don’t rely on PaperRater for anything involving AI content. It’s not built for that.
Check out our AI Detector and Humanizer in the widget below!
FAQs About PaperRater
Can the PaperRater plagiarism checker be used to check both academic papers and blog posts?
Technically yes. You can submit any type of writing. But the plagiarism detection works the same regardless of document type, which means it has the same limitations.
For academic papers, you’re better off using a tool that checks against academic databases. For blog posts, you want something that verifies originality more thoroughly than PaperRater’s basic web search.
The grammar checking might be slightly more helpful for blog posts since it flags readability issues and overly complex sentences. But again, the suggestions aren’t always accurate. You’ll need to review each one manually.
What document types does the PaperRater plagiarism checker support?
You can select from several categories, including essay, research paper, term paper, dissertation, journal article, book review, and more. But this selection mainly affects how the scoring algorithm weights certain factors.
The actual checking process is the same. You’re pasting text into a web form. It doesn’t matter if you call it an essay or a dissertation. The tool doesn’t actually understand document structure or academic conventions differently based on your selection.
You also can’t upload documents directly and have to copy and paste your text. No Word doc uploads. No PDF scanning. Just plain text in a box.
This is less convenient than tools that integrate with Google Docs or accept file uploads, and also more tedious if you’re checking longer documents.
Final Verdict
PaperRater is a basic, free tool that does some things adequately and other things poorly.
It catches obvious grammar mistakes, like the ones you could probably find yourself if you read carefully. It provides a readability score that might be useful if you’re writing for a specific grade level.
But the plagiarism detection is unreliable. Missing two-thirds of the copied content in our test? That’s unacceptable if you’re depending on it for important work.
Students could submit plagiarized essays. Bloggers could accidentally publish copied content. Teachers could miss cheating.
The complete absence of AI detection makes it outdated. In 2025, checking for AI-generated content is essential. PaperRater doesn’t even try. It can’t tell the difference between human writing and ChatGPT output.
For quick proofreading of a casual email? Sure, use PaperRater. For anything that matters? You need better tools.
Undetectable AI offers comprehensive protection. You can:
- Detect AI content in your work
- Rewrite flagged sections to pass detection
- Paraphrase sources properly
- Generate original content that passes all checks
The reality is that writing in 2025 involves navigating AI detection, plagiarism checking, and grammar standards. PaperRater only handles one of those three, and it doesn’t even do that one reliably.