HTTP/1.1 200 OK Server: nginx/1.9.10 Date: Tue, 12 Apr 2016 02:05:15 GMT Content-Type: text/html; charset=UTF-8 Content-Length: 14459 Connection: keep-alive X-Powered-By: PHP/5.6.18-1+deb.sury.org~trusty+1 Link: ; rel=webmention
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header. The URL is relative, so this will also test whether your discovery code properly resolves the relative URL.