The best free tech stack detectors, ranked
By Philipp Kant 4 min read
A tech stack detector is a tool that identifies the software behind a website, such as the CMS, shop system, frameworks, analytics, and hosting, by matching known fingerprints in the page source, asset URLs, response headers, and cookies. Free detectors run as browser extensions on the page you are viewing or as web lookups for any URL.
People use them for three jobs: sales teams qualifying leads by the software a company runs, developers sizing up a migration or a competitor, and site owners finding out what an agency actually installed years ago.
| Tool | Runs as | Strength | Free tier |
|---|---|---|---|
| Wappalyzer | Extension + web lookup | Broad, well-maintained fingerprints | Free account, 50 lookups a month |
| BuiltWith | Web lookup + extension | Technology history over years | Free lookups, paid lead lists |
| WhatRuns | Browser extension | Quick look, plugin names | Free |
| Netcraft Site Report | Web lookup | Hosting, network, TLS history | Free |
1. Wappalyzer, the reference fingerprint set
Wappalyzer is the best-known detector and still the broadest. It recognizes thousands of technologies across CMS, shop systems, JavaScript frameworks, analytics, payment, and hosting, and shows them grouped by category with version numbers where the page reveals them.
The free account includes 50 technology lookups a month. Lead lists, monitoring, and bulk lookups are paid plans aimed at sales teams.
2. BuiltWith, the history
BuiltWith’s free lookup shows what a site runs today and, its real strength, what it ran before: when the shop moved from one platform to another, when a tracking tool was added or dropped. That history explains the shape of a site better than a snapshot.
The interface is dense and pushes its paid lead lists hard. For one-off lookups the free tier is enough.
3. WhatRuns, the quick look while browsing
WhatRuns is a free browser extension that lists the technologies on the page you are viewing in one click, and it is good at naming WordPress plugins and themes. Nothing to type, no account.
It only works on the page in your browser tab, and its coverage of less common tools is thinner than Wappalyzer’s.
4. Netcraft Site Report, the infrastructure view
Netcraft looks below the page: hosting provider, network owner, IP history, TLS certificate details, and the web server. When the question is where a site is hosted rather than what it renders with, this is the free tool to use.
It says little about the CMS, plugins, or marketing tags.
How detection works, and why it misses things
Every detector works the same way: it compares what a site exposes against a library of known patterns.
| Signal | Example | What it reveals |
|---|---|---|
| Asset paths | /wp-content/plugins/ |
WordPress and its plugins |
| HTML markers | a generator meta tag |
CMS and version |
| Script hosts | cdn.shopify.com |
Shop platform |
| Cookies | _ga, _fbp |
Google Analytics, Meta pixel |
| Headers | server, x-powered-by |
Web server, hosting |
That method has blind spots by design:
- Backend systems are invisible. The ERP, the PIM, the CRM behind the shop expose nothing to a browser.
- Hidden fingerprints. Sites that strip version tags, bundle their scripts, or proxy assets through their own domain look like “unknown”.
- Consent-gated tags. Trackers that load only after cookie consent are missing from a detector that never clicks “accept”.
- Stale guesses. A leftover script from a removed tool still counts as “uses X”.
What the stack tells you
A detector’s list is a starting point, not a verdict. Two questions turn it into something useful:
- What does it cost? Each analytics tag, chat widget, and pixel adds weight. The list above maps directly onto what slows the page; see the best free website speed tests.
- What runs before consent? Every marketing tool on the list is a privacy question in the EU. See the best free cookie scanners.
FAQ
How can I find out what a website is built with? Run the URL through Wappalyzer or BuiltWith, or open the page with the WhatRuns extension. For hosting, use Netcraft’s site report.
What is the best free Wappalyzer alternative? BuiltWith for history, WhatRuns for a quick look while browsing, Netcraft for infrastructure. No single free tool covers all three.
How accurate are tech stack detectors? Accurate for what a page exposes, blind to what it hides. A detected tool is almost always really there; a missing one may be bundled, proxied, or loaded only after consent.
Can a detector see a site’s ERP or CRM? No. Backend systems leave no trace in the HTML. At most a form endpoint or a tracking script hints at the CRM.
We built our own free Tech Stack Detector: one URL in, and it reads the HTML, asset URLs, response headers, and cookies to name the CMS, shop system, frameworks, analytics, marketing pixels, consent tool, payments, and hosting, plus the WordPress plugins and theme visible in asset paths. Full disclosure, it is ours, and it needs no signup. Knowing the stack is the first step of any migration or integration, and the step after it is what we do.
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