Flask is a lightweight, synchronous WSGI framework ideal for traditional web applications and rapid prototyping, while Starlette is a modern, async-first ASGI framework built for high-performance APIs and real-time applications. Flask has 15+ years of ecosystem maturity; Starlette excels in concurrent request handling with native async/await support.
Flask vs Starlette — Side-by-side comparison on A Versus B
Lightweight Python web microframework for building web applications with minimal overhead.
Modern async-first Python ASGI web framework optimized for building high-performance APIs and real-time applications.
Async Support. Concurrent Requests Handling. Community & Ecosystem Size. Built-in Features. Learning Curve. Production Deployment Complexity. WebSocket Support
Choose Flask if you're building traditional web applications, prioritize ecosystem maturity, need extensive third-party extensions, or are learning Python web development—its simplicity and 15-year ecosystem make it ideal for MVPs and monolithic apps. Choose Starlette if you're building high-concurrency APIs, microservices, real-time applications with WebSockets, or need async/await patterns—its ASGI foundation and modern async architecture deliver superior performance for I/O-bound workloads.
Flask: None (use SQLAlchemy separately) | Starlette: N/A
Flask: Requires manual or third-party setup | Starlette: N/A
Flask: No (use Flask-Login or similar) | Starlette: N/A
Flask: Manual integration required | Starlette: N/A
Flask: Experimental in Flask 2.0+ | Starlette: Yes (built-in)
Flask: No, requires add-ons | Starlette: N/A
Flask: Python 2.7+ (legacy) / 3.4+ | Starlette: N/A
Flask: Extension required (Flask-SocketIO) | Starlette: Built-in native support
Flask: Native (NumPy, TensorFlow, Pandas) | Starlette: N/A
Flask: Via SQLAlchemy extension | Starlette: N/A
Flask: ~2,500 RPS | Starlette: ~7,500 RPS
Flask: 23,500 positions | Starlette: N/A
Flask: 500 optimal | Starlette: 5,000+ optimal
Flask: No, manual setup required | Starlette: No (manual or third-party tools)
Flask: 10,000+ extensions | Starlette: N/A
Flask: Yes (Werkzeug-based) | Starlette: N/A
Average Community Response Time (GitHub Issues)
Flask: ~4,000 req/s | Starlette: ~8,500 req/s
Flask: Synchronous (WSGI) | Starlette: Asynchronous (ASGI)
Flask: ~75 (baseline with Gunicorn 4 workers) | Starlette: ~4,500 (with Uvicorn async)
Flask: ~150,000+ PyPI packages | Starlette: N/A
Flask: Native: NumPy, Pandas, Scikit-learn, TensorFlow, PyTorch | Starlette: N/A
Flask: No - requires WSGI server (Gunicorn, uWSGI) | Starlette: N/A
Flask: 350 lines (with extras) | Starlette: N/A
Third-party Packages Required (typical CRUD)
Flask: 6/10 (more decisions) | Starlette: N/A
Job Market Demand (LinkedIn postings 2026)
Flask: Requires Flask-APScheduler or manual async setup | Starlette: N/A
Flask: Manual (requires Flask-RESTX, Flasgger) | Starlette: N/A
Flask: 2-3 days | Starlette: 5-7 days (requires async knowledge)
Flask: ~90,000 Flask-compatible packages | Starlette: ~8,000 Starlette-compatible packages
Flask: ~70,000 | Starlette: ~9,500 stars
Flask: No (WSGI-based) | Starlette: Yes (ASGI-based)
Flask: Requires external WSGI server | Starlette: N/A
Flask: N/A | Starlette: ~1.2M (Jan 2026)
Flask: N/A | Starlette: Low-level ASGI web framework
Flask: N/A | Starlette: ~18,000-22,000 req/sec
Flask: N/A | Starlette: None (manual required)
How to choose between Flask and Starlette
Flask vs Starlette — Structured Comparison Data
Machine-readable comparison dataset for Flask vs Starlette. Contains 102 attribute comparisons, 5 FAQ pairs.
Flask vs Starlette — Attribute Category Vocabulary
Taxonomy of attribute categories used to classify comparison data for Flask vs Starlette.
Flask 2.0+ added native coroutine support for view functions, but it still runs on WSGI which doesn't natively support async. You'd need to use an ASGI server and quart (Flask's async equivalent) or add async extensions. Starlette has async as its core architecture, making it the better choice if async is essential.
Which framework has better performance for handling concurrent users?
Starlette with Uvicorn handles 50-60x more concurrent requests than Flask with Gunicorn (4,500+ vs 75 req/sec). Flask uses multi-process concurrency (overhead-heavy), while Starlette's async model handles thousands of concurrent connections in a single process. For high-traffic APIs, Starlette wins decisively.
Is Flask dead? Should I learn Starlette instead?
Flask is not dead—it remains the most-used Python web framework (67,000 GitHub stars vs Starlette's 9,500) and receives regular maintenance. Choose Flask for traditional web apps and learning; Starlette for modern async APIs. Most companies use both: Flask for monoliths, Starlette for microservices.
Can I build a real-time app (chat, notifications) with Flask?
Yes, with Flask-SocketIO extension, but it's more complex. Starlette has WebSocket support built-in, making real-time features simpler to implement. For production chat apps, Starlette + Uvicorn is recommended due to better async handling and cleaner WebSocket API.
Which framework is easier for beginners?
Flask is significantly easier for beginners. Its synchronous, straightforward request/response model is intuitive, and you can build a functional app in 2-3 days. Starlette requires understanding async/await patterns, making it better suited for intermediate Python developers. Start with Flask if you're new to web development.
How to Choose Between Flask and Starlette
Async Support: Flask has Limited (WSGI-based, sync-only), while Starlette has Native (ASGI-based, async-first).
Concurrent Requests Handling: Flask has ~50-100 requests/sec (single-threaded baseline), while Starlette has ~5,000+ requests/sec (async with uvicorn).
Community & Ecosystem Size: Flask has ~90,000+ packages on PyPI that extend Flask, while Starlette has ~8,000+ packages (growing ecosystem).
Built-in Features: Flask has Routing, templating, session management included, while Starlette has Routing, middleware; templating requires Jinja2 integration.
Learning Curve: Flask has Beginner-friendly (2-3 days to productivity), while Starlette has Intermediate (requires async/await knowledge).
Consider: Production Deployment Complexity
Production Deployment Complexity: Flask has Simple with Gunicorn/uWSGI (multi-process), while Starlette has Simple with Uvicorn (single async worker).
WebSocket Support: Flask has Requires Flask-SocketIO extension, while Starlette has Built-in native support.