# README.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

## Project Overview

AI Fact Checker - a full-stack web application that verifies claims using Natural Language Inference (NLI) models. The system searches the web via SerpAPI, analyzes snippets against claims, and returns verdicts (True/False/Ambiguous) with evidence.

## Tech Stack

**Backend (Python/Flask):**
- Flask REST API with CORS
- ML: HuggingFace Transformers (RoBERTa, mDeBERTa-v3)
- Translation: deep_translator (Google Translate)
- Database: SQLite with caching layer
- Search: SerpAPI for Google search results

**Frontend (React/Vite):**
- React 19 with Vite 7
- React Router for navigation
- Axios for HTTP requests
- CSS custom properties for theming

## Architecture

```
factchecker/
├── backend/
│   ├── app.py          # Flask API, NLI logic, model switching
│   ├── database.py     # SQLite cache, verified facts, stats
│   ├── .env            # SERPAPI_API_KEY (required)
│   └── venv/           # Python virtual environment
├── frontend/
│   ├── src/
│   │   ├── App.jsx     # Router setup
│   │   ├── main.jsx    # React entry point
│   │   ├── components/
│   │   │   └── Layout.jsx
│   │   └── pages/
│   │       ├── Home.jsx    # Main fact-check UI
│   │       └── About.jsx
│   └── package.json
└── factchecker.db      # SQLite database (auto-created)
```

## Key Commands

### Backend
```bash
cd backend
source venv/bin/activate  # or: venv\Scripts\activate on Windows
python app.py             # Start Flask on port 5000
python clear_cache.py     # Clear cache
python view_db.py         # View database contents
```

### Frontend
```bash
cd frontend
npm install
npm run dev               # Vite dev server
npm run build             # Production build
npm run lint              # ESLint
```

## API Endpoints

- `POST /api/check` - Verify a claim (body: claim, language, dateFrom, dateTo, selectedSource, model)
- `GET /api/history` - Get check history (query: limit)
- `GET /api/stats` - Get database statistics
- `POST /api/admin/add-fact` - Add manually verified fact (admin)

## Models

Dva NLI modely dostupné s rôznymi компромismi:
1. **RoBERTa** (`ynie/roberta-large-snli_mnli_fever_anli_R1_R2_R3-nli`) - Rýchly, vyžaduje preklad do angličtiny
2. **mDeBERTa** (`MoritzLaurer/mDeBERTa-v3-base-xnli-multilingual-nli-2mil7`) - Najlepší pre slovenčinu, multilingválny

## Database Schema

- `fact_checks` - Cached results with claim hash, verdict, NLI votes, evidence, sources
- `verified_facts` - Manually verified facts (admin-added)

## Important Notes

- The `.env` file contains the SerpAPI key - do not commit
- Models are loaded on-demand; switching triggers reload with cache clearing
- Slovak claims are auto-translated for RoBERTa; mDeBERTa handles Slovak natively
- Domain whitelist/blacklist filters search results for quality
- Results are cached by claim hash to avoid redundant API calls