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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 tens of millions of 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, which by 2024 had expanded to include CliffsNotes, Course Hero, LitCharts, Scribbr, Symbolab, LanguageTool, and Bartleby.
QuillBot is headquartered in Chicago, Illinois, at 303 East Wacker Drive, Suite 2101. The product is offered as a web application at quillbot.com, a Chrome extension with more than 6 million users, a free Microsoft Word add-in, and dedicated apps for macOS, Windows, iOS, and Android.
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 distinct business units. As of 2023, Learneo's portfolio included Course Hero, QuillBot, CliffsNotes, LitCharts, Scribbr, and Symbolab. Learneo later acquired LanguageTool in March 2023 to further strengthen its AI writing capabilities, and in May 2023 it acquired the Digital Student Solutions (DSS) segment of Barnes & Noble Education, which added Bartleby and Student Brands to the portfolio. By 2024, Learneo described itself as operating eight brands, served more than 100 million monthly active users across the group, and reported combined revenue exceeding $200 million.
Rohan Gupta continued to lead QuillBot as its CEO under the Learneo umbrella.
Following the rebranding, QuillBot moved aggressively beyond its original paraphraser into a broad suite of free AI writing utilities. New capabilities released in 2024 and 2025 included an AI-augmented translator with explanations of grammar and word choice, a refreshed AI detector capable of distinguishing fully AI-written, AI-refined, and human-authored text, and an expanded library of standalone generators (cover letters, business plans, character descriptions, product launch copy, and more) hosted on the quillbot.com/ai-writing-tools hub.
In August 2025, QuillBot launched a Team Style Guide feature for its Teams plan, allowing organizations to define and enforce a shared tone, vocabulary, and formatting rules across users. In October 2025 the company added a tenth paraphrasing mode informally branded "Boomer Mode," which converts Gen Z and internet slang into more conventional professional language, and rolled out an AI Character Generator and a Speech to Text feature. The same month, QuillBot adjusted its pricing for the first time in years, raising the headline annual plan to $99.95 per year (an effective $8.33 per month) and the standalone monthly plan to $19.95.
In November 2025, QuillBot updated its privacy policy to begin storing text inputs from desktop users in order to personalize results and train future models, with opt-out controls available in account settings. The change drew criticism from some academic and privacy commentators, particularly those handling sensitive student or client work, and is one of several flashpoints in the broader debate over how AI writing tools should treat user content.
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. The work, authored by Brendan Chambers and David Silin together with collaborator Kevin Gimpel of the Toyota Technological Institute at Chicago, addresses the practical problem that billion-parameter models impose heavy hardware, energy, and latency costs at production scale. By training smaller "student" models to replicate the behavior of much larger "teacher" models, QuillBot can deliver real-time paraphrasing and grammar suggestions without sacrificing output quality, and at a unit cost low enough to support a generous free tier.
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 platform relies heavily on GPU-backed inference clusters, with smaller distilled models handling the bulk of free-tier traffic and larger models reserved for premium modes such as Academic, Formal, and the AI Humanizer.
Since the Learneo restructuring, QuillBot's NLP stack has been deployed inside several sibling brands. The free paraphrasing tool on Scribbr.com is powered by QuillBot's models, and Scribbr's AI Detector is, according to both companies, a wrapper around QuillBot's underlying detector. This sharing arrangement lets Learneo invest in a single AI research group while reaching audiences with very different brand identities (academic editing on Scribbr, multilingual proofreading on LanguageTool, and student writing assistance on QuillBot).
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.
As of 2026 the paraphraser exposes ten 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 |
| Boomer | Converts Gen Z and internet slang into conventional professional language (added October 2025) | 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, and it is one of the features QuillBot most directly markets as a competitor to Grammarly.
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, and is distinct from the Turnitin-backed plagiarism check offered by sister brand Scribbr.
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. A 2024 update added explanatory annotations covering sentence structure, word choice, and verb conjugation, positioning the translator as a learning tool for ESL students rather than a pure machine-translation service.
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. It also supports bulk document uploads and is targeted explicitly at GPT-5- and Gemini-class outputs in QuillBot's marketing.
Independent benchmarks of the detector have produced a wide range of results, depending on the type and length of input. Reported accuracy figures include roughly 64% on machine-generated content in one 2025 audit, 78 to 91% across other 2025 reviews, and 92 to 98% on raw, unedited AI text in a separate test set. Reviewers consistently note two limitations: accuracy drops sharply once AI text has been paraphrased or hand-edited, and the detector exhibits a non-trivial false-positive rate on human writing (one test reported around 35%). For comparison, GPTZero and Turnitin have reported above-90% detection rates on similar benchmarks. These caveats have led most academic guidance to treat any AI-detector verdict as a signal for further investigation rather than as proof of misconduct.
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. The humanizer is a controversial feature: while QuillBot positions it as a way to soften the stiff, formulaic register of large language model output, it is also widely used as an explicit AI-detector evasion tool and has drawn criticism from educators and from competing detection vendors.
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.
In parallel with its core suite, QuillBot operates a collection of free, single-purpose generators at quillbot.com/ai-writing-tools. The hub includes a cover letter generator, an AI business plan generator, an AI character generator (added October 2025), a product launch copy generator, an essay outline generator, an email writer, and dozens of similar utilities. Most run without a sign-up. The hub serves both as an SEO funnel for QuillBot's premium subscriptions and as a way for the company to test specialized prompts before promoting them into the main product.
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 (available via the Microsoft AppSource marketplace) that integrates the paraphraser and grammar checker as a sidebar within Word for Windows, Mac, and Word on the web |
| macOS app | Desktop application for Mac users with system-wide pop-up integration |
| Windows app | Desktop application that surfaces QuillBot inside Slack, Outlook, and other Windows apps |
| iOS app | Mobile writing assistant and keyboard app for iPhone and iPad |
| Android app | Native Android app providing paraphrasing and grammar checking on mobile |
According to QuillBot's listing on the Chrome Web Store, the Chrome extension has been installed by more than 6 million users as of 2025, up from roughly 2 million users at the time of the Course Hero acquisition. The extension works across most websites and activates as a floating widget that appears alongside text input fields.
QuillBot operates on a freemium model. Following an October 2025 price adjustment, the headline tiers are:
| Plan | Price | Key Features |
|---|---|---|
| Free | $0 | Paraphraser (Standard and Fluency modes), grammar checker, summarizer (limited), translator, basic AI humanizer |
| Premium (monthly) | $19.95/month | All paraphrasing modes, unlimited custom modes, plagiarism checker, advanced AI humanizer, priority processing |
| Premium (semi-annual) | ~$6.66/month ($39.95 every 6 months) | Same Premium feature set, billed twice a year |
| Premium (annual) | $8.33/month ($99.95/year) | Same Premium feature set, billed once a year |
| Student | $6.25/month (annual, requires .edu email) | All Premium features at a student discount |
| Teams | $7.50/user/month (2-10 seats, billed annually) | All Premium features plus Team Style Guide, centralized billing, and admin controls; volume discounts available for 11+ seats |
All paid plans include a 3-day money-back guarantee. Approximately 60% of QuillBot's subscription revenue comes from annual plan subscribers. The 2025 price increase, in which the headline annual plan rose from roughly $49.95 per year to $99.95 per year and the monthly plan from $9.95 to $19.95, was the largest pricing change in the company's history and was applied gradually to existing customers via grandfathered renewals.
User-count claims for QuillBot vary widely across sources and time periods. The company stated in 2022 that more than 150 million people had used QuillBot at least once, while early-2024 disclosures cited 75 million registered users worldwide spread across more than 190 countries. The platform attracts roughly 25 million monthly active users and processes over 100 million paraphrasing queries per month. The discrepancy between the 150 million and 75 million figures appears to reflect different methodologies (cumulative visitors versus registered accounts) rather than a decline in user base.
Key user demographics reported by QuillBot and third-party analytics providers 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 |
| GPTZero | AI content detection | Specialized detector frequently cited as a benchmark for QuillBot's own AI Detector |
Compared to Grammarly, QuillBot offers lower pricing for premium plans and more robust paraphrasing capabilities with its ten-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. Within Learneo, QuillBot also overlaps with LanguageTool (for grammar) and Scribbr (for academic editing), but the parent company has positioned each brand at a different point on the price/specialization curve rather than treating them as direct rivals.
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.
The arrival of generative-AI detectors has added a second layer to the debate. Tools such as Turnitin, GPTZero, and QuillBot's own AI Detector now flag suspected machine-generated text, while QuillBot's AI Humanizer is openly marketed (and widely used) as a way to make AI output less detectable. This has produced a continuous "arms race" between detectors and humanizers, with each side updating models in response to the other. Researchers studying the dynamic have warned that reliance on automated detectors carries a meaningful risk of false accusations, particularly against non-native English writers, and most institutional policy bodies now recommend pairing any detector verdict with human review and student dialogue.
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.
For most of its history QuillBot processed text inputs on the fly without retaining them. In November 2025 the company updated its privacy policy and product behavior so that text submitted from desktop clients (web, Word add-in, and desktop apps) is now stored on QuillBot servers and may be used to personalize results and to train future models. Users can opt out of training use in account settings, and Teams plan administrators retain organization-level controls. The change brought QuillBot into closer alignment with how most other major AI writing tools handle user content but drew pushback from some academic and legal users, who treat client text as confidential. QuillBot also publishes a Trust Center page covering encryption in transit and at rest, role-based access controls, and SOC 2 audit status.
Reviewers generally describe QuillBot as the most polished and accessible paraphrasing tool on the market, with particular praise for the multi-mode paraphraser, the synonym slider, and the breadth of the free tier. The Chrome extension is consistently rated as one of the best free writing utilities for use inside Gmail, Google Docs, and LinkedIn. Critics, on the other hand, point to several recurring weaknesses: the AI Detector's variable accuracy, the AI Humanizer's mixed reliability, the inability to generate original long-form content from a brief or keyword (a gap that competitors such as Jasper AI fill), and the price increases introduced in late 2025. Capterra and G2 user ratings sit in the 4.4 to 4.6 range out of 5, and Trustpilot ratings hover near 4.7 out of 5.