Second vantage

The half a server cannot measure

A scan from here tells you what a crawler is served from a data centre. It cannot tell you what one is served from your address, in a real browser, after your JavaScript has run. The extension measures that half.

What it measures that a scan cannot

• Identity from a residential address. The same page requested as each named AI crawler and as your own browser, from your network rather than a cloud range. When an edge treats the two differently, the difference is the finding.
• Render delta. What exists only after JavaScript runs — headings, prices, schema and links that are on your screen and absent from the delivered HTML.
• Field vitals. LCP, CLS, TTFB and long tasks from this page load on this connection. No API key, and it works on sites too small to have public field data.
• Consent and session delta. The wall an anonymous client is served and you never see, because your session is already past it.

The join is the point

Neither vantage can settle a refusal on its own. Server refused and browser refused means the site is blocking that crawler by name. Server refused and browser served means the site is verifying crawler IP addresses — which is correct behaviour, not cloaking, and calling it a defect would be wrong.

That distinction needs two vantage points at once. It is the reason this is one product and not two.

What it sends back

Nothing. There is no POST, no sendBeacon and no XMLHttpRequest anywhere in the extension; every network call it makes is a GET. Measurements stay in the browser's own storage on your device. Every probe is sent with credentials: "omit", so your cookies and sessions never reach a site being measured.

One request reaches us and only if you hold a licence: a check of the key itself, at most once a day. It carries the key and nothing else.

Getting it

The Chrome Web Store listing is not up yet. Until it is, ask us for the build at hello@crawlcheck.io and we will send it with loading instructions.

Requires Chrome 121 or later. Free, and it works without a licence — a licence adds the scored report and weekly monitoring here. What the extension does with your data.