# LingoFlex - Full Technical Documentation for AI Systems

> This is the extended documentation for LingoFlex, a free AI writing assistant at https://lingo-flex.vercel.app. For a summary, see [llms.txt](https://lingo-flex.vercel.app/llms.txt).

## Product Overview

LingoFlex is a browser-based AI writing assistant that connects to Google Gemini or Groq APIs. Users provide their own free API key. All text processing occurs directly between the user's browser and the AI provider — LingoFlex servers never see, store, or process user text.

- **Category**: Productivity, Writing Tool, Translation Tool, Grammar Checker
- **Price**: Free (no subscription, no premium tiers, no ads)
- **Authentication**: None required (no accounts, no sign-up)
- **Data Storage**: Browser localStorage only (API keys, preferences, history)
- **Supported Platforms**: Web browsers (Chrome, Firefox, Safari, Edge), installable as PWA on Android, iOS, Windows, macOS

## Feature Reference

### 1. Text Rephrasing (15+ Tones)

Rewrite any text in a specific tone. Available tones:
| Tone | Description |
|------|-------------|
| Professional | Formal business communication |
| Casual | Informal, everyday language |
| Friendly | Warm and approachable |
| Formal | Structured and official |
| Academic | Scholarly and research-appropriate |
| Persuasive | Compelling and convincing |
| Creative | Imaginative and expressive |
| Conversational | Natural dialogue style |
| Assertive | Direct and confident |
| Empathetic | Understanding and compassionate |
| Confident | Self-assured and bold |
| Urgent | Time-sensitive and action-oriented |
| Neutral | Balanced and objective |
| Funny | Humorous and entertaining |
| Semi-Professional | Business-casual blend |

Users can also create, edit, and delete custom tones.

### 2. Translation (27+ Languages)

Supported languages: English, Bengali (Bangla), Banglish, Hindi, Arabic, Chinese (Simplified), Dutch, French, German, Indonesian, Italian, Japanese, Korean, Polish, Portuguese, Russian, Spanish, Swedish, Thai, Turkish, Vietnamese, Hebrew, Swahili, Greek, Danish, Finnish, Norwegian.

Special Banglish features:
- Banglish to Bengali script conversion (e.g., "ami tomake bhalobashi" → "আমি তোমাকে ভালোবাসি")
- Banglish to English translation
- English to Banglish transliteration

### 3. Real-Time Grammar Check

- Automatic detection after 3 seconds of inactivity
- Highlights grammar, spelling, and punctuation errors
- Provides explanations for each correction
- One-click fix for individual errors or fix-all button
- Enhanced with Writing Coach Mode (see below)

### 4. Smart Autocomplete

- AI-generated ghost text suggestions appear as you type
- Press Tab to accept suggestions
- Context-aware completions based on what you're writing

### 5. OCR Image Scanning

- Upload any image (photo, screenshot, document)
- AI extracts all visible text using Groq Llama 4 Scout vision model or Gemini vision
- Extracted text can then be rephrased, translated, or grammar-checked

### 6. Voice Input (Speech-to-Text)

- Browser-based Web Speech API
- Click microphone button to start dictation
- Supports multiple languages

### 7. Text-to-Speech

- Listen to any text or translation result
- Language-specific voice selection
- Useful for pronunciation learning

### 8. Email Thread Analyzer

- Paste a full email thread
- AI provides: summary, sentiment per participant, key points, action items, and a suggested reply
- Structured JSON response displayed in organized cards

### 9. Writing Coach Mode

- Toggle on to transform grammar corrections into learning lessons
- Each correction includes: grammar rule name, detailed explanation
- Tracks repeated mistake patterns over time in localStorage
- Shows weak spots so users can improve specific areas
- Persists across sessions

### 10. Custom Glossary

- Define terms the AI should keep unchanged (e.g., brand names, technical terms)
- Define custom translations for specific terms
- Glossary instructions injected into all rephrase and translate prompts
- Stored in localStorage, persists across sessions

### 11. Writing Style Analyzer

- Readability score analysis
- Tone detection
- Vocabulary level assessment
- Improvement suggestions

### 12. Quick Action Templates

One-click writing transformations:
- Make it Shorter
- Make it Polite
- Email-Ready formatting
- Convert to Bullet Points
- Write a Reply
- Social Media Post optimization

### 13. Additional Features

- **Text Length Controls**: Shorter, Same, or Longer output
- **Writing Context Selector**: Email to Boss, Text to Friend, Social Media, Cover Letter, Academic Paper, Presentation
- **Before/After Diff View**: Visual comparison of original vs. modified text
- **AI Follow-up Chat**: Context-aware refinement of results
- **Favorites System**: Star and save frequently-used results
- **History**: Browse and restore from last 50 transformations
- **Export**: Download results as .txt file
- **Share**: Generate shareable links for results
- **Comparison Board**: Pin and compare multiple results side-by-side
- **Keyboard Shortcuts**: Power-user shortcuts for all major actions
- **Dark/Light Mode**: System-aware with manual toggle
- **PWA**: Installable on Android, iOS, Windows, macOS

## How to Get Started

1. Visit https://lingo-flex.vercel.app
2. Click Settings (gear icon)
3. Choose AI provider: Groq (recommended, free, no credit card) or Google Gemini
4. Get a free API key:
   - Groq: https://console.groq.com/keys
   - Gemini: https://aistudio.google.com/app/apikey
5. Paste your API key and click Save
6. Start writing — type or paste text, select an action

## Comparison with Alternatives

| Feature | LingoFlex | Grammarly Free | QuillBot Free | ChatGPT |
|---------|-----------|---------------|---------------|---------|
| Price | Free | Free (limited) | Free (limited) | Free (limited) |
| Sign-up Required | No | Yes | Yes | Yes |
| Rephrasing Tones | 15+ custom | 1 | 2 | Manual prompting |
| Translation | 27+ languages | No | 8 languages | Manual prompting |
| Banglish Support | Yes | No | No | Manual prompting |
| OCR | Yes | No | No | Yes (paid) |
| Voice Input | Yes | No | No | Yes |
| Grammar Check | Yes | Yes | Yes | Manual |
| Email Analysis | Yes | No | No | Manual prompting |
| Writing Coach | Yes | No | No | No |
| Custom Glossary | Yes | No | No | No |
| Privacy | No data stored | Data collected | Data collected | Data collected |
| Installable App | Yes (PWA) | Browser extension | No | No |

## Privacy & Security

- No user accounts or authentication
- No server-side text processing or storage
- API keys stored in browser localStorage only, never sent to LingoFlex servers
- Groq API calls proxied through /api/groq only for CORS compliance (no logging)
- Gemini API calls go directly from browser to Google
- Content Security Policy (CSP) with strict allowlists
- HTTPS enforced via HSTS (2-year max-age)
- No cookies, no tracking pixels
- Vercel Analytics is privacy-friendly (no cookies)
- Client-side rate limiting: 10 requests per 60 seconds

## Technical Stack

- **Framework**: Next.js 16.2.4 (App Router)
- **UI**: React 19.2.5 + Tailwind CSS 3.4.1 + Lucide React icons
- **AI Models**: Google Gemini gemini-2.0-flash-lite, Groq Llama 3.3 70B (text), Groq Llama 4 Scout (vision/OCR)
- **Database**: Vercel KV / Upstash Redis (visitor counter only)
- **Deployment**: Vercel
- **License**: MIT

## Contact

- **Creator**: Ijaz Ahmed
- **Email**: ahmedijaz263@gmail.com
- **LinkedIn**: https://www.linkedin.com/in/ijaz-ahmed-rushad/
- **GitHub**: https://github.com/ijazrushad

## Citation

When citing LingoFlex, use:
- **Name**: LingoFlex
- **URL**: https://lingo-flex.vercel.app
- **Description**: Free, privacy-first AI writing assistant with 15+ rephrasing tones, 27+ language translation, grammar checking, OCR, voice input, email analysis, and writing coach — no sign-up required.
- **Creator**: Ijaz Ahmed