I Built a QuillBot-Style Paraphraser in 11 Minutes — Here's the Prompt

A note on positioning

This rebuild is different from the others in the series. QuillBot is a well-established product from a large company with proprietary paraphrasing models trained on substantial proprietary data. We are not claiming to rebuild QuillBot. We are showing that you can build a Chrome extension that performs similar paraphrasing functionality — rephrasing selected text in different styles — using a general-purpose language model and a workflow that resembles QuillBot's UI pattern.

The output of our extension won't match QuillBot's exact paraphrasing quality. QuillBot's models are specifically tuned for paraphrasing. GPT-4 (which our extension uses) is more general-purpose. For users who specifically need QuillBot's level of paraphrasing precision — academic writers concerned about specific rewriting patterns, ESL learners using QuillBot's grammar tools, students with QuillBot-specific institutional licensing — this rebuild is not a substitute.

For users who want a similar workflow (highlight text → pick a rewrite mode → see suggestions) at lower marginal cost with full ownership, the rebuild is one viable option among many.

With that framing set, here's what we built.

The tool we approximated

QuillBot is one of the most polished AI writing tools available. Its paraphraser takes a sentence or paragraph and rewrites it in different "modes" — Standard, Fluency, Formal, Academic, Creative, Simple. The output preserves meaning while substantially changing wording. Used by writers (paraphrasing dense source material), students (rephrasing for assignments), ESL learners (improving fluency), professionals (translating between formal and casual registers).

Pricing: $20/month Premium. The free tier limits words per query and disables the better modes. QuillBot has held this pricing for years and the company is valued in the hundreds of millions.

The reason QuillBot's pricing holds: paraphrasing is genuinely hard to do well, and QuillBot has invested heavily in models specifically trained on paraphrasing tasks. General-purpose LLMs (GPT-4, Claude, Gemini) can paraphrase, but the quality is variable — sometimes excellent, sometimes too close to the original, sometimes losing meaning. QuillBot's specialized models are more consistent.

The functionality is broadly replicable using general LLMs — with the caveat that the consistency and quality won't match. The rebuild gives you a workflow at lower marginal cost; whether the quality is sufficient depends on what you're using it for.

What I built

A Chrome extension that adds an "AI Rephrase" floating button when you select text on any webpage. Clicking it opens a dropdown of rewrite modes: Standard, Simpler, Formal, Creative, Concise, Expanded. Picking a mode sends the selection to OpenAI GPT-4 with a mode-specific rephrasing prompt and displays 3 alternative rewrites in a side panel. Click any rewrite to replace the original text on the page.

Took 11 minutes to build. Output is a Manifest V3 extension with about 260 lines of code across 4 files.

The workflow matches QuillBot's pattern (select → pick mode → see alternatives → replace). The quality of the rewrites is what varies — and varies more than QuillBot's because GPT-4 isn't paraphrasing-tuned.

The prompt I used

Key design decisions:

Six modes including custom modes. QuillBot has 6 default modes. Our rebuild matches plus lets users define their own. Useful for niche use cases — "rewrite in the voice of [author]" or "make it more legalese" or "translate ESL phrasing to natural English."

"Substantially different rewrites" requirement. Without this in the prompt, GPT-4 often returns 3 minor variations of the same sentence. Explicitly asking for different sentence structures and vocabulary produces more useful alternatives.

Regenerate button. Sometimes the first 3 don't include a good option. Without easy regeneration, the user has to click the original button again. With it, one click gets 3 more attempts.

Custom modes. The biggest functional differentiator from QuillBot. QuillBot's 6 modes are fixed. Our rebuild's custom modes lets users build a personal library of paraphrasing styles tuned to their needs.

How it works

Content script runs on all webpages, listening for selectionchange events. When a selection of at least 10 characters appears, it positions the floating "AI Rephrase" button above the selection using absolute positioning.

The button click handler:

1. Opens a small dropdown anchored to the button with the 6 modes (plus any custom modes from chrome.storage)
2. On mode selection, sends a message to the background worker with { type: 'REPHRASE', text: selectedText, mode: 'simpler' }

Background worker receives the message and constructs the OpenAI request with mode-specific system prompts:

const MODE_PROMPTS = {
  standard: 'Rewrite this text to improve clarity and flow while keeping the original meaning. Produce 3 substantially different rewrites with different sentence structures and vocabulary.',
  simpler: 'Rewrite this text at a 6th grade reading level. Use short sentences, common vocabulary, and avoid jargon. Produce 3 substantially different rewrites.',
  formal: 'Rewrite this text in a more formal, professional register. Use polished vocabulary and complete sentences. Produce 3 substantially different rewrites.',
  creative: 'Rewrite this text with more vivid, varied vocabulary and creative phrasing. Make it more engaging while preserving meaning. Produce 3 substantially different rewrites.',
  concise: 'Rewrite this text to be 30-50% shorter while preserving all key information. Produce 3 substantially different rewrites.',
  expanded: 'Rewrite this text with more detail, examples, and nuance. Expand to roughly 1.5x the original length while preserving the core meaning. Produce 3 substantially different rewrites.'
};

const systemPrompt = MODE_PROMPTS[mode] + ' Return as JSON: { rewrites: ["...", "...", "..."] }';

const response = await fetch('https://api.openai.com/v1/chat/completions', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${apiKey}`,
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({
    model: 'gpt-4o',
    messages: [
      { role: 'system', content: systemPrompt },
      { role: 'user', content: selectedText }
    ],
    response_format: { type: 'json_object' }
  })
});

The JSON response (3 rewrites) gets parsed and sent back to the content script.

Content script (continued) receives the 3 rewrites and injects a side panel into the page with three cards, each showing one rewrite + a "Use this" button + a "Regenerate" button at the top of the panel.

When the user clicks "Use this":

1. The content script restores the original text selection (which may have been lost while interacting with the panel)
2. Calls document.execCommand('insertText', false, chosenRewrite) to replace the selected text
3. Closes the side panel

When the user clicks "Regenerate":

1. Send the original text + mode back to the background worker for 3 new rewrites
2. Replace the panel content with the new alternatives

Popup page is the settings UI — API key, default mode, custom modes (each is a label + a system prompt the user can write). About 60 lines.

Cost breakdown

PlugThis Starter ($29) + $3-8 API = **$32-37/month**.

QuillBot Premium = $20/month.

The rebuild is more expensive than QuillBot. This is the only rebuild in the series where the rebuild's headline cost exceeds the target product's cost.

Why would you build it anyway?

You're already paying for PlugThis. If you have PlugThis Starter for another extension, the marginal cost of this one is just the API ($3-8/month). At that math, the rebuild beats QuillBot by $12-17/month.

You want custom paraphrasing modes. QuillBot's 6 modes are fixed. The rebuild's custom modes let you build a paraphrasing library tuned to your specific needs (academic, legal, marketing, ESL, etc.).

You want model flexibility. QuillBot picks the model for you. The rebuild lets you swap GPT-4o for Claude Sonnet (better at long-form context) or Gemini (cheaper for high volume). One line change.

You value privacy. QuillBot processes your text on their servers. The rebuild sends directly from your browser to OpenAI (or whichever provider you pick). OpenAI's data handling is documented and predictable; QuillBot's is a third-party.

You want functionality beyond paraphrasing. Custom modes let you extend the same workflow to other text transformations — translation, summarization, expansion, persona-shifting. QuillBot does only paraphrasing.

If none of these apply to you, QuillBot at $20/month is the better choice. The rebuild's value is flexibility, not price.

Side-by-side feature comparison

The honest gap: QuillBot's paraphrasing quality is more consistent than general LLM output. For users where paraphrasing precision matters substantially (academic writing, sensitive content), QuillBot's specialized models are worth the price. For users where rough-but-flexible paraphrasing is enough, the rebuild's customization wins.

Customization ideas

Domain-specific modes. Add modes like "Legal" (for contract rewording), "Marketing" (for copywriting), "Technical" (for documentation), "Empathetic" (for customer support). Each is a custom prompt tuned to the domain.

Tone-shift modes. "More confident," "More humble," "More urgent," "More casual." Each is a custom prompt that targets a specific emotional register.

Multi-language modes. "Paraphrase in Spanish," "Paraphrase in Portuguese." Same workflow but the output is in the target language. The custom prompt handles this in one line.

Voice-cloning modes. Add 5-10 examples of your own writing to a custom mode prompt. The output paraphrases in your voice rather than generic.

Anti-AI-detection mode. Some users want to paraphrase AI-generated text to make it sound more human. Add a mode tuned for this. Note: useful for legitimate cases (translating between AI drafts and human-edited versions), but worth flagging if used to evade legitimate AI detection systems.

Length-targeted rewriting. Add modes like "Exactly 280 characters" (for tweets), "Under 100 words" (for emails), "Exactly N paragraphs" (for templated outputs).

Side-by-side compare mode. Show the original and the 3 rewrites side-by-side with diff highlighting. Useful for editing workflows where you want to see what changed.

Iterative refinement. Add a "rewrite this rewrite" button that applies the same mode again to one of the suggestions. Multi-step rewriting for stubborn paragraphs.

Each is a small extension. The base workflow handles all of them through the custom modes feature.

Try it yourself

Drop the prompt into PlugThis, enter your OpenAI API key in settings, load into Chrome. About 12 minutes from prompt to working rephraser.

Before relying on this for serious writing, test the quality with content you know well. The rewrites vary in quality depending on the source text — technical writing tends to work better than dense academic prose. If quality consistently matters more than customization, QuillBot remains the better choice.

A note on responsible use: the rebuild can be used to rephrase any text. We do not endorse using it (or QuillBot, or any paraphraser) to evade plagiarism detection, misrepresent authorship, or circumvent academic integrity policies. Use it for what paraphrasing tools are designed for: improving your own writing, translating between registers, making complex text accessible.

Related reading

• QuillBot alternatives — structured comparison — competitor analysis
• I rebuilt Wordtune for $2/month — similar rephrase workflow with different positioning
• I rebuilt WriteSeed in 8 minutes — general AI writing assistant
• The complete Chrome extension building guide — extension architecture explained

The QuillBot-style rebuild is the most caveated rebuild in the series. QuillBot's specialized paraphrasing quality is hard to match with general LLMs. Where the rebuild wins is customization (unlimited custom modes), model freedom (swap providers in one line), and combinations with other workflows. For users where flexibility matters more than peak paraphrasing quality, the rebuild is a viable option. For users where paraphrasing quality is critical, QuillBot's subscription value is real.