# How to Vibe Code Your Own Wordtune (and Stop Paying for It)

> Express yourself with confidence

- Site: https://wordtune.com
- Category: SaaS
- Platforms: Web app, Browser extension, iOS app
- Verdict: **Solid side project** (68/100 vibecodeable)
- Estimated effort: 2-3 weeks part-time

## Verdict

Build a personal web app and extension wrapper around an LLM API to handle rewriting and summarization, but skip trying to replicate the proprietary foundational models and brittle multi-site browser DOM injection.

You can build a fully functional personal clone of Wordtune's core loop—paraphrasing, tone adjustment, and summarization—in a web editor using Next.js and the Vercel AI SDK. However, building a universal browser extension that injects floating UI into arbitrary web applications like Google Docs and Slack without breaking their event handlers is a notoriously painful maintenance nightmare. Expect to spend significant debugging hours handling extension manifest permissions, cross-origin content script isolation, and managing LLM response latency to make inline rewriting feel snappy.

### What you can't replicate

- AI21 Labs' proprietary foundational models (Jurassic/Jamba)
- Deep enterprise integrations and long-tail optimizations across every web platform
- The massive proprietary dataset of 780M+ user-selected rewrite patterns

## What it does

An AI-powered writing companion, reading assistant, and paraphrasing tool that helps users rewrite text, adjust tone, check grammar, summarize documents, and translate languages.

### Core features

- Sentence & paragraph paraphrasing with tone selection (casual/formal) and length adjustment
- Real-time spelling and grammar error highlighting and correction
- AI text continuation ('Continue writing') and contextual elaboration ('Spices')
- RAG-backed fact-checking with external web source attribution
- Document, article, and YouTube video summarization
- Smart translation from foreign languages directly into edited English

## The business

### Pricing

- Basic: $0.00 — For limited use spelling and grammar corrections
- Advanced: $4.89/mo — For perfect writing with daily limits
- Unlimited: $6.99/mo — Unlimited writing assistance anywhere

### Funding

$636M raised.
- Seed (2019): $9.5M
- Series A (Nov 2021): $25M
- Series B (July 2022): ~$64M
- Series C (Late 2023): $208M
- Series D (May 2025): $300M
Investors: Google, Nvidia, Intel Capital, Pitango First, Ahren Innovation Capital, Comcast Ventures, Samsung Next

Founded 2017.
Team size: ~200 employees (AI21 Labs).

## The hard parts

- Cross-platform browser extension content scripts reliably injecting overlays into complex editable DOMs (Google Docs canvas, Slack contenteditable divs) without breaking host app behavior
- Low-latency streaming LLM responses to provide inline suggestions without noticeable typing lag
- Robust web-scraping and multi-source RAG grounding pipeline for fact-checking ('Spices')
- Managing token limits and context windows efficiently for long document/video summarization

## How to vibe code Wordtune

### Prerequisites

- Node.js (free): Required runtime for Next.js development and local package management.
- GitHub (free): Source control and deployment pipeline integration.
- Anthropic API Key (pay-as-you-go (~$5-10/mo)): Powers the high-reasoning text rewriting, tone shifting, and summarization engines.

### Recommended AI tools

- Claude Code: Best-in-class terminal agent for scaffolding the full-stack Next.js app, setting up API routes, and writing browser extension content scripts.
- Cursor: Ideal for fine-tuning the React UI components, editor widgets, and extension popup views with direct diff reviews.

### Stack

- Frontend: Next.js with Tailwind CSS and shadcn/ui
- Backend: Next.js Server Actions / API Routes with Vercel AI SDK
- Database: Turso (SQLite at the edge for saving user snippet history)
- Auth: better-auth
- Payments: None (personal use clone)
- Other: Vercel AI SDK for streaming LLM rewrites, Firecrawl for fetching and scraping reference web URLs for summarization, WebExtension APIs (Manifest V3) for the browser extension popup wrapper

### Hosting

- Vercel (Hosting the Next.js web application and API endpoints with zero-config deploys.): $0/mo (Hobby Tier)
- Turso (Serverless SQLite database storing user saved text snippets and rewrite history.): $0/mo (Free Tier)

### Build guide

1. **Project Scaffolding & Database Setup** — Initialize the Next.js project with Tailwind CSS, configure shadcn/ui components, and set up Turso SQLite with better-auth for personal authentication.

```
Scaffold a new Next.js 16 application using App Router, TypeScript, and Tailwind CSS. Integrate Turso via libSQL for data storage and install better-auth for local user authentication. Create a clean dashboard layout with a sidebar for writing history, saved snippets, and settings.
```

2. **Core Editor & Rewrite Engine** — Build the primary web editor interface where users can paste or type text, highlight segments, and trigger AI rewrite actions.

```
Build a rich-text writing editor page in Next.js using a clean, distraction-free textarea or content-editable canvas. Implement a floating toolbar that appears when text is highlighted. Add control pills for tone adjustment ('Casual', 'Formal'), length adjustment ('Shorten', 'Lengthen'), and a primary 'Rewrite' button that calls a backend API route streaming structured alternatives.
```

3. **Streaming AI Rewriting API with Vercel AI SDK** — Implement the backend API route using the Vercel AI SDK and Anthropic API to generate contextual rewrites, tone shifts, and grammatical corrections.

```
Implement a Next.js API route using the Vercel AI SDK and Anthropic Claude Sonnet. Create server actions that accept source text, target tone, and mode (rewrite, shorten, lengthen, grammar_check). Construct robust system prompts ensuring the model returns a JSON array of 3 distinct, high-quality alternatives while preserving the original intent.
```

4. **Summarizer & Fact-Checking Subsystem** — Add article and URL summarization capabilities with grounding checks.

```
Create a dedicated 'Summarizer' view where users can input a raw URL or paste long-form text or transcripts. Integrate Firecrawl API to extract markdown text cleanly from web pages. Use the AI SDK to generate bulleted executive summaries with key takeaways and extract source citations.
```

5. **Browser Extension Manifest V3 Wrapper** — Build a lightweight browser extension that communicates with your hosted Next.js backend to provide quick rewriting popups.

```
Scaffold a Manifest V3 browser extension directory containing a background service worker, a popup UI React app, and a content script. The content script should detect highlighted text on web pages, display a small floating icon button next to the selection, and open a popup modal showing streamed rewrite alternatives fetched from your deployed Next.js backend API.
```

6. **Polish, Error Handling & Deployment** — Refine UI states, loading skeletons, error handling for rate limits, and deploy to Vercel.

```
Add comprehensive error boundaries, loading skeletons during LLM streaming, and toast notifications for copy-to-clipboard actions across the web app and extension popup. Optimize the production build, configure environment variables for production API keys, and prepare deployment files for Vercel.
```

### Cost vs paying

**Starting costs (one-time):**

- Anthropic API Developer Credits: $10.00
- Total: ~$10.00 one-time

**Ongoing costs (monthly):**

- Anthropic API Usage (Personal Volume): ~$3-5/mo
- Hosting & Database (Vercel + Turso free tiers): $0/mo
- Total: ~$3-5/mo

- Paying for the SaaS instead: $9.99/mo (Unlimited Plan)
- Build time: 25-35 hours
- AI tool credits: $20/mo (Claude Pro / Cursor)
- Break-even: Never (built for learning and personal utility)

## Sources

- [Wordtune Official Website](https://wordtune.com)
- [AI21 Labs Wikipedia](https://en.wikipedia.org/wiki/AI21_Labs)