Is This Website Built With Flask?

How to Tell if a Website Uses Flask

Identifying whether a website was built with Flask used to require technical expertise — inspecting source code, tracing network requests in DevTools, and knowing which patterns to look for. Our free scanner automates all of that: it fetches the page, analyzes 1 Flask-specific signals, and returns a verdict with a confidence score.

You might want to detect Flask for competitive research, due diligence before acquiring a site, or simple curiosity. Whatever the reason, this page covers every method — automated and manual.

What is Flask?

Flask is a minimalist Python web framework popular for prototypes, internal APIs, and small-to-medium applications where developers want full control without a large framework's conventions imposed on them. Flask has no distinctive markup or cookie signature by default, so AIWebsiteDetector relies on the `Werkzeug` banner Flask's built-in development server sends in its `Server` response header — a strong signal when present, but one that's typically absent once a Flask app is deployed behind a production WSGI server like gunicorn, so Flask is more reliably detected on demos and prototypes than on hardened production deployments.

It is primarily used for powering websites built by developers using AI coding assistants or modern JavaScript frameworks.

Visit Flask official website

How to Manually Detect Flask Websites

Method 1 — View Page Source

Open the website in your browser
Press Ctrl+U (Windows) or Cmd+Option+U (Mac)
Search (Ctrl+F) for flask or flask
If found in script src, class names, or meta tags — it's likely Flask

Method 2 — Browser DevTools Network Tab

Press F12 to open DevTools
Click the Network tab and reload the page
Filter by flask in the search box
If you see requests to Flask-specific domains, it's confirmed

Faster: Skip the manual steps — paste the URL into our scanner above and we check all 1 signals in seconds.

How Our Flask Detector Works

When you submit a URL, our engine fetches the page from its server — just like a browser would — then analyzes the response across 1 Flask-specific fingerprints:

Script analysis

We scan all loaded JavaScript files for known CDN paths and runtime names

CDN domain matching

We cross-reference every asset request against known platform CDNs

HTML pattern scanning

We search the DOM for platform-specific class names and data attributes

Header inspection

We read HTTP response headers that identify the server or platform

Meta tag extraction

We check generator and other meta tags in the document head

Confidence scoring

We weight each matched signal and normalize to a 0–99% score

Frequently Asked Questions

How can I tell if a website was built with Flask?

The most reliable ways to detect Flask are: (1) open DevTools → Network tab and look for requests to Flask-specific CDN domains, (2) view page source and search for Flask-specific class names or data attributes, (3) use our free scanner — we check 1 detection signals automatically and return a confidence score.

Is your Flask detector free?

Yes, completely free. Paste any URL into our scanner and we'll analyze it for Flask fingerprints immediately. No account required, no limits on scans.

How accurate is the Flask detection?

We check 1 unique Flask fingerprint signals across HTML, JavaScript, CDN domains, meta tags, and HTTP headers. Our confidence score reflects how many signals matched — a score above 70% is a strong indicator. We cap accuracy at 99% to reflect that all fingerprint-based detection is probabilistic.

Can Flask sites be detected if they use a custom domain?

Yes. Custom domains don't hide the underlying platform. The JavaScript files, CDN requests, HTML attributes, and server headers all remain identifiable regardless of the domain name used. Our scanner fetches the page directly and analyzes its technical composition.

What should I do after detecting a Flask website?

If you want to build something similar, visit https://flask.palletsprojects.com to learn more or sign up. If you're doing competitive research, our scan result also shows the full technology stack — including hosting platform, domain age, and other detected technologies. You can share the result link with your team.