No signup, nothing stored. Checking somebody else's site is fine: this only reads what every visitor's browser already downloads.
This checks the page your address serves to a normal visitor, the same way a browser would, and it opens any Google Tag Manager container it finds and reads inside it. Nothing is stored, no signup is asked for, and the answer is the same one you would get by opening the page source yourself with more patience than most people have.
What each answer actually tells you
WordPress means somebody probably paid an agency once and was left to maintain it, so plugins age and security updates stop. Wix, Squarespace, GoDaddy and Duda mean the site is rented: it works, and it stops working the month the subscription lapses. Shopify means there is a real store behind it. Webflow usually means a designer was involved. None of these are wrong choices, but they predict different problems.
The free address is the most useful thing this finds
If a site is still on something like yourname.wixsite.com or a godaddysites.com address, the owner has never bought a domain. Every business card, van and Google listing is pointing at an address they do not own and cannot take with them. It also reads badly to a customer comparing three quotes, in a way most owners have never had anyone say out loud to them.
Addresses that have already been switched off
Google turned business.site off in 2024. Any business still handing out a business.site link is losing every visitor who taps it, and because the owner never taps their own link they usually have no idea. This check flags that case separately, because it is not a website problem, it is a website that no longer exists.
How to check it by hand
Open the page source with Ctrl+U and search for wp-content for WordPress, wixstatic for Wix, squarespace for Squarespace, cdn.shopify for Shopify, or wsimg.com for GoDaddy. The fingerprints are in the asset URLs because every builder serves its images and scripts from its own domain, which is also why they cannot be hidden.
Common questions
Can a site hide what it is built with?
Mostly no. A builder serves scripts and images from its own servers, and those addresses appear in the page. A custom build can genuinely look like nothing in particular, which is why the honest answer for those is that no fingerprint was found rather than a guess at a name.
Is one platform better than another?
For a small local business, the platform matters far less than whether the site loads fast on a phone and whether a visitor can contact you in one tap. A fast Wix site beats a slow custom build every time.
Why does it matter if the site is on a free subdomain?
Because the address is not yours. You cannot move it, you cannot sell the business with it, and if the platform closes your account the address stops working. Buying a domain is roughly the cost of a coffee a month and it is the one thing worth doing immediately.
Does this work on any website?
It works on any page that loads for a normal visitor. Sites behind a login, behind aggressive bot protection, or that are simply down will return an error rather than a guess.