Flask
Flask is a Python micro web framework ideal for rapidly constructing web applications, offering minimalism, flexibility, and modularity.
What detecting Flask tells you about a site
Flask is Python's minimalist micro-framework — it ships almost nothing by default, which paradoxically makes it harder to fingerprint than Django. The most reliable tell is the default session cookie: a session cookie whose value is a base64 payload with a dotted signature segment, set without Django's CSRF pairing. Add a Server header naming Werkzeug (Flask's dev WSGI server) on non-production deployments. Detecting Flask suggests a small, deliberately un-opinionated Python service — an API, a microservice or a lightweight app where the team wanted to assemble its own stack rather than adopt Django's conventions.
Flask in a real-world stack
When you find Flask, it rarely travels alone. Gunicorn or uWSGI in production, SQLAlchemy for data access, and frequently a separate front end since Flask leaves templating optional.
About
Flask is a Python micro web framework ideal for rapidly constructing web applications, offering minimalism, flexibility, and modularity.
Categories: Web frameworks, Web servers
Quick facts
Detection methodology for Web frameworks
Server software identification reads the `Server` response header and (where exposed) version-specific markers in error pages. Cloudflare in front of nginx in front of Apache is the classic three-layer stack you'll see in the wild — we surface each layer separately so the actual origin server isn't masked by the edge layer.
How we detect Flask
Sourcemap Explorer carries 1 fingerprint signal for Flask, spread across 1 channel — response header. The exact patterns are listed below, and you can replay each one in Chrome DevTools to confirm a match by hand.
Each signal alone is rarely conclusive — Sourcemap Explorer cross-references all of them and weights by confidence. You can reproduce any of these checks yourself in Chrome DevTools.
Server-side fingerprint: the response header reveals the technology behind the page. Visible in DevTools → Network → response headers.
Server: Werkzeug/?([\d\.]+)?
Implies
When Flaskis detected, Sourcemap Explorer also marks the following technologies as present (Wappalyzer's implies graph).
FAQ
How do I check if a website is using Flask?
Open the page in Chrome, click the Sourcemap Explorer toolbar icon, and read the Stack tab. Flask's specific fingerprints here are response header, and the popup flags Flask whenever any combination of them is found. The same checks can be reproduced manually in DevTools — see the "How we detect" section above.
What Flask version can Sourcemap Explorer detect?
Flask ships as a hosted web frameworks rather than a bundled npm package, so version-specific detection isn't always possible. Where the platform leaks a version in response headers (`X-Powered-By`, `Server`, generator meta tags) we surface it; otherwise we report presence only.
Is Flask open source?
Yes, Flask is open source. The license details are listed on the official site (https://github.com/pallets/flask/), and the codebase typically lives on a public source-control host.
Where can I read more about Flask?
Official site: https://github.com/pallets/flask/. For Sourcemap Explorer's detection guide, see the deep-dive link below or the related guides in the cross-link section.
Keep reading on Sourcemap Explorer
Alternative tools
Detected by Sourcemap Explorer
Open the popup on any page running Flaskand you'll see the exact version pulled from the bundled package.json when sourcemaps are exposed.