Our checker and your server

If you found NosHostCheck in your logs, someone used one of our tools to check your site. This page explains what those requests are.

Why we connected to your server

We do not crawl the web. Every request is started by a person running a check on this site, such as a redirect check, an SSL check or a security headers check, for a URL on your domain. Usually that person is you or someone who works on your site.

What the requests look like

• Most checks send a single GET request and stop reading after the headers. The Meta Tag Checker reads up to 1 MB of the page. The Robots.txt Tester reads /robots.txt.
• Redirect checks follow up to 20 redirects, one request each.
• SSL checks open a few TLS connections to read the certificate and test which protocol versions you support. They do not send HTTP requests.
• The user agent always contains NosHostCheck/1.0. Some tools let the visitor imitate a browser or a search engine crawler, in which case NosHostCheck is added to the end of that user agent.
• Identical checks are cached for a short time, and each visitor's checks are rate limited, so one person cannot send a flood of requests.

robots.txt

Because each request is a one-off check asked for by a person, like someone opening your page in a browser, the tools do not follow robots.txt rules. The Robots.txt Tester only reads the file to show what it says.

Blocking our requests

You can block requests whose user agent contains NosHostCheck in your web server or firewall. For example, in Nginx:

if ($http_user_agent ~* "NosHostCheck") {
    return 403;
}

Our tools will then report a 403 response for your site.

Report a problem

If you see requests that do not match this description, email [email protected] with the times and the IP address from your logs.