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.
The tag on the page is only half of it
Google Ads needs two things: the global tag loading on the site, and a conversion action defined in the Ads account that something on the site actually triggers. This check can see the first from outside. The second lives inside your account, under Goals, then Conversions, then Summary. If that list is empty or every row says 'No recent conversions', the tag is loading and reporting nothing, which looks identical to a healthy account until you open that page.
Why a campaign with no conversion data costs more per customer
Smart Bidding decides what a click is worth from conversion history. With no conversions coming back, there is no history, so the strategy falls back to buying clicks as cheaply as it can. Cheap clicks and valuable clicks are not the same clicks. This is the single most common reason a small advertiser reports that Google Ads brought traffic but no work.
The tag was there, then a site redesign happened
The commonest way this breaks is a rebuild. A new theme, a new page builder, a new developer, and the tag that lived in the old footer never gets carried across. Spending carries on uninterrupted because nothing about the ads changes, and the conversion column quietly goes to zero. Anyone who rebuilds a site should re-run this check the same day it goes live.
How to check it by hand
Open the site, press Ctrl+U for the source, and search for googleadservices.com or AW-. If you find nothing but you do find googletagmanager.com, the tag is probably inside the container and you need to open the container in Tag Manager to see. That second step is the one most free checkers skip, which is why they report a missing tag on sites that have one.
Common questions
Is the Google Ads tag the same as Google Analytics?
No. They are separate tags with separate IDs. GA4 uses G- and Google Ads uses AW-. Having one does not give you the other, although they can be linked so that Ads can import conversions defined in Analytics.
My Ads account shows conversions. Do I still need this?
Then the important part is already working. This is most useful when the conversion column reads zero and nobody is sure whether the problem is the ads, the website or the measurement, because it rules the measurement in or out in ten seconds.
Does this tell me how much I am spending?
No. It reads only what your public page loads. Spend, keywords and conversion actions are all inside your Ads account and nothing outside it can see them.
It says cannot tell. What now?
There is a Tag Manager container on the page that could not be opened, so the tag may well be inside it. Open the container in Tag Manager and look at the tag list. Saying no here would be a guess.