flask

# Flask Skill

Production-tested patterns for Flask with the application factory pattern, Blueprints, and Flask-SQLAlchemy.

**Latest Versions** (verified January 2026):
- Flask: 3.1.2
- Flask-SQLAlchemy: 3.1.1
- Flask-Login: 0.6.3
- Flask-WTF: 1.2.2
- Werkzeug: 3.1.5

---

## Quick Start

### Project Setup with uv

```bash
# Create project
uv init my-flask-app
cd my-flask-app

# Add dependencies
uv add flask flask-sqlalchemy flask-login flask-wtf python-dotenv

# Run development server
uv run flask --app app run --debug
```

### Minimal Working Example

```python
# app.py
from flask import Flask

app = Flask(__name__)

@app.route("/")
def hello():
    return {"message": "Hello, World!"}

if __name__ == "__main__":
    app.run(debug=True)
```

Run: `uv run flask --app app run --debug`

---

## Project Structure (Application Factory)

For maintainable applications, use the factory pattern with blueprints:

```
my-flask-app/
├── pyproject.toml
├── config.py                # Configuration classes
├── run.py                   # Entry point
│
├── app/
│   ├── __init__.py          # Application factory (create_app)
│   ├── extensions.py        # Flask extensions (db, login_manager)
│   ├── models.py            # SQLAlchemy models
│   │
│   ├── main/                # Main blueprint
│   │   ├── __init__.py
│   │   └── routes.py
│   │
│   ├── auth/                # Auth blueprint
│   │   ├── __init__.py
│   │   ├── routes.py
│   │   └── forms.py
│   │
│   ├── templates/
│   │   ├── base.html
│   │   ├── main/
│   │   └── auth/
│   │
│   └── static/
│       ├── css/
│       └── js/
│
└── tests/
    ├── conftest.py
    └── test_main.py
```

---

## Core Patterns

### Application Factory

```python
# app/__init__.py
from flask import Flask
from app.extensions import db, login_manager
from config import Config


def create_app(config_class=Config):
    """Application factory function."""
    app = Flask(__name__)
    app.config.from_object(config_class)

    # Initialize extensi