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QuillBot is an artificial intelligence-powered writing platform that provides paraphrasing, grammar checking, summarization, plagiarism detection, citation generation, translation, and AI content detection tools. Founded in 2017 by three computer science students at the University of Illinois at Urbana-Champaign (UIUC), the platform grew from a single paraphrasing tool into a comprehensive writing assistant used by over 75 million registered users worldwide. QuillBot was acquired by Course Hero (later renamed Learneo) in August 2021 and operates as part of Learneo's portfolio of learning and productivity brands.
QuillBot is headquartered in Chicago, Illinois, at 303 East Wacker Drive, Suite 2101.
QuillBot was co-founded in 2017 by Rohan Gupta, Anil Jason, and David Silin. The three founders met as computer science students at UIUC. Anil Jason and David Silin had previously collaborated on several hackathons together, winning 11 consecutive hackathon competitions. Anil Jason and Rohan Gupta connected through UIUC's iVenture Accelerator program.
The original motivation for building QuillBot came from Anil Jason, who wanted to create a tool that could help English Language Learner (ELL) students improve their writing. After recruiting Gupta and Silin, the team built the first version of QuillBot's paraphraser. Rohan Gupta serves as CEO, Anil Jason as CTO, and David Silin as CSO.
Shortly after launch, QuillBot went viral on Reddit, attracting a rapid influx of early users. The founders then entered UIUC's iVenture Accelerator, where they won initial funding to continue developing the platform. During this period, the company operated on a bootstrapped basis, reinvesting revenue to grow the product.
In April 2020, QuillBot closed a $4.25 million seed funding round led by Sierra Ventures and GSV Ventures, with participation from Service Provider Capital, AI Venture Labs, and TBD Ventures. Prior to this round, the company had been entirely bootstrapped by its founders. The seed funding allowed the team to expand its engineering workforce and accelerate feature development beyond the original paraphrasing tool.
By 2020, QuillBot had already begun experiencing significant user growth, driven in part by the shift to remote learning during the COVID-19 pandemic. Students and professionals increasingly turned to online writing tools, and QuillBot benefited from this broader trend.
On August 19, 2021, Course Hero announced the acquisition of QuillBot. The financial terms of the deal were not publicly disclosed. At the time of the acquisition, QuillBot had raised a total of approximately $4.34 million across its funding rounds and had already amassed millions of active users.
The acquisition placed QuillBot alongside other Course Hero properties, including CliffsNotes and LitCharts. Following the acquisition, Course Hero raised a $380 million Series C round in December 2021 at a $3.6 billion valuation, led by Wellington Management with participation from Sequoia Capital Global Equities, OMERS Growth Equity, and D1 Capital Partners.
In December 2022, Course Hero co-founder Andrew Grauer announced the creation of a new parent company called Learneo, Inc. The rebranding was made public in May 2023. The move reflected the company's expansion from a single educational platform into a portfolio of six distinct business units. As of 2023, Learneo's portfolio includes Course Hero, QuillBot, CliffsNotes, LitCharts, Scribbr, and Symbolab. Learneo later acquired LanguageTool in 2023 to further strengthen its AI writing capabilities.
Rohan Gupta continued to lead QuillBot as its CEO under the Learneo umbrella.
QuillBot's tools are built on natural language processing (NLP) techniques and deep learning algorithms. At the core of the platform are transformer-based language models, similar in architecture to models in the GPT family, that analyze the semantics and context of input text before generating alternative phrasings or corrections.
The system processes text through several stages:
QuillBot's models are trained on large datasets covering grammar, spelling, punctuation, tone, sentence structure, and clarity. The company has stated that its language models are "carefully fine-tuned on human-curated internal data, and interwoven with additional components" beyond standard pre-training on public text corpora. This fine-tuning process allows the models to handle different writing styles and tones across the platform's various modes.
QuillBot's engineering team has published research on compressing large language generation models using sequence-level knowledge distillation. This technique involves training smaller, faster "student" models to replicate the behavior of larger "teacher" models, enabling QuillBot to deliver real-time performance at scale without sacrificing output quality.
QuillBot runs on Google Cloud infrastructure. According to a Google Cloud case study, QuillBot has scaled its infrastructure up to 100 times its original capacity to handle growing user demand, processing over 100 million paraphrasing queries per month.
The paraphraser is QuillBot's flagship tool and the product that launched the company. It rewrites input text while preserving the original meaning, offering users multiple ways to express the same idea. The tool is free to use with no account required, and there is no limit on the number of paraphrases a user can run.
The paraphraser offers nine predefined modes plus unlimited custom modes for premium subscribers:
| Mode | Description | Availability |
|---|---|---|
| Standard | Replaces words with synonyms and rearranges word order while maintaining meaning | Free |
| Fluency | Improves clarity and readability of the text | Free |
| Formal | Rewrites text in a professional tone suitable for workplace or academic contexts | Premium |
| Academic | Adjusts text for a scholarly or research-focused tone | Premium |
| Simple | Simplifies complex language for general audiences | Premium |
| Creative | Allows greater deviation from the source text for more varied output | Premium |
| Expand | Elaborates on the text, adding more detail and length | Premium |
| Shorten | Condenses the text while retaining key information | Premium |
| Custom | User-defined modes with configurable parameters | Premium |
A "Synonym Slider" control lets users adjust the degree of change applied to the text. Moving the slider to the left produces a more conservative rephrase with fewer word changes; moving it to the right generates a more creative output with more extensive modifications.
QuillBot's grammar checker identifies and corrects errors in spelling, grammar, punctuation, and sentence structure. The tool uses AI-powered analysis to provide inline suggestions, highlighting errors directly in the text and offering one-click fixes. The grammar checker is available for free on QuillBot's website and through its browser extensions.
The plagiarism checker uses machine learning algorithms to compare submitted text against a database of published works, web pages, and academic papers. The tool analyzes both the wording and the semantic content of the text to detect potential instances of unattributed borrowing. Results include a percentage score and highlighted passages that match existing sources. The plagiarism checker is a premium feature with a limited number of free scans available.
The summarizer condenses long documents, articles, or papers into shorter versions while retaining the critical information and core message. Users can adjust the summary length and choose between a "Key Sentences" mode (which extracts the most important sentences from the original text) and a "Paragraph" mode (which generates a new condensed paragraph).
QuillBot's citation generator creates formatted citations in APA, MLA, and Chicago style. Users can generate both full bibliographic citations and in-text citations. The tool supports citations for books, journal articles, websites, and other source types. As of early 2024, the citation generator had processed over 12 million citation checks.
The translator supports over 50 languages, allowing users to translate text between language pairs. The tool uses AI-based machine translation and is integrated into the broader QuillBot platform, so users can translate text and then immediately paraphrase or grammar-check the output.
QuillBot's AI content detector analyzes text to estimate the likelihood that it was written by a human or generated by an AI system such as ChatGPT, GPT-4, or Gemini. The detector classifies each section of text into one of four categories: AI-generated, AI-generated and AI-refined, human-written and AI-refined, or human-written. Independent testing has shown that QuillBot's AI detector correctly identified approximately 64% of machine-generated content, compared to rates above 93% for specialized detectors like GPTZero and Turnitin.
The AI humanizer tool transforms AI-generated text into more natural, human-sounding language by adjusting tone, clarity, and flow without changing the underlying meaning. The humanizer supports multiple languages, including Spanish, German, French, and Portuguese, as well as four English dialects (US, UK, Australian, and Canadian). A basic version is available for free, with an advanced mode available to premium subscribers.
QuillBot Flow (formerly known as Co-Writer) is an integrated writing workspace that combines research, note-taking, citation generation, paraphrasing, grammar checking, and AI-powered text suggestions into a single environment. Key features include:
Flow is designed for students, researchers, and content creators who want to write, research, and edit without switching between multiple applications.
QuillBot is available through several platforms and integrations:
| Platform | Description |
|---|---|
| Web application | Full suite of tools available at quillbot.com |
| Chrome extension | Provides grammar checking and paraphrasing on Gmail, Google Docs, LinkedIn, Outlook, Slack, Confluence, Notion, Facebook, X (formerly Twitter), and other websites |
| Microsoft Word add-in | Free add-in that integrates the paraphraser and grammar checker as a sidebar within Microsoft Word |
| macOS app | Desktop application for Mac users |
| iOS app | Mobile writing assistant and keyboard app for iPhone and iPad |
The Chrome extension has been installed by over 2 million users. The extension works across most websites and activates as a floating widget that appears alongside text input fields.
QuillBot operates on a freemium model with several pricing tiers:
| Plan | Price | Key Features |
|---|---|---|
| Free | $0 | Paraphraser (Standard and Fluency modes), grammar checker, summarizer (limited), translator, basic AI humanizer |
| Premium | $19.95/month (monthly), $13.33/month (semi-annual), $8.33/month (annual) | All paraphrasing modes, unlimited custom modes, plagiarism checker, advanced AI humanizer, priority processing |
| Student | $6.25/month | All Premium features at a 25% discount (requires .edu email) |
| Teams | $7.50/user/month | All Premium features for groups of 2 to 10 users |
All paid plans include a 3-day money-back guarantee. Approximately 60% of QuillBot's subscription revenue comes from annual plan subscribers.
As of early 2024, QuillBot reports 75 million registered users worldwide across more than 190 countries. The platform attracts approximately 25 million monthly active users, with over 100 million paraphrasing queries processed each month.
Key user demographics include:
QuillBot holds an estimated 18% market share in the AI writing tools sector and ranks as the second-largest paraphrasing tool globally by user base. The platform has a 4.7 out of 5 rating on Trustpilot.
QuillBot competes with several other AI writing tools, each with a different primary focus:
| Competitor | Primary Focus | Key Differentiator |
|---|---|---|
| Grammarly | Grammar, spelling, and style checking | Comprehensive proofreading with tone detection and style guides |
| Wordtune | Sentence-level rewriting and tone adjustment | Focuses on enhancing existing writing rather than catching errors |
| ProWritingAid | Long-form writing analysis | In-depth reports on writing style, readability, and consistency |
| Jasper AI | AI content generation | Designed for marketing teams and long-form content creation |
| Spinbot | Quick bulk text spinning | Minimal interface for fast, no-frills paraphrasing |
| LanguageTool | Multilingual grammar checking | Supports over 30 languages; now a Learneo sibling brand |
Compared to Grammarly, QuillBot offers lower pricing for premium plans and more robust paraphrasing capabilities with its nine-mode system. Grammarly, by contrast, provides stronger grammar and style checking features, tone detection, and a larger integration ecosystem. Many writers use both tools for complementary purposes.
QuillBot's paraphrasing capabilities have raised questions about academic integrity, particularly in educational settings. The central concern is that students may use the tool to rephrase copied content in order to bypass plagiarism detection software such as Turnitin.
Some educators have identified a practice called "patchwriting," in which students combine paraphrased snippets from multiple sources into what appears to be original text. While the wording changes, the underlying ideas remain unattributed, which constitutes plagiarism under most academic honor codes.
Institutional responses have varied. Universities such as Harvard and Stanford have updated their honor codes to address AI tool usage, generally allowing tools like QuillBot for drafting purposes but requiring disclosure when submitting final work. Other institutions have taken stricter positions: some consider text altered through paraphrasing software to be a form of academic misconduct, with penalties including course failure.
QuillBot's own help center addresses the question directly, stating that the tool is designed to help users improve their writing skills rather than to facilitate cheating. The company positions QuillBot as a learning aid comparable to a thesaurus or style guide, arguing that its proper use involves understanding and engaging with the content being paraphrased.