Debug

location / {
    add_header Content-Type text/plain;
    return 200 $document_root;
}

location / {
    add_header Content-Type text/plain;
    return 200 "document_root: $document_root, request_uri: $request_uri";
}

add_header X-uri "$uri";

location ~* ^.+.(jpg|jpeg|gif|css|png|js|ico|html|xml|txt)$ {
    add_header X-debug-message "A static file was served" always;
    ...
}

location ~ \.php$ {
    add_header X-debug-message "A php file was used" always;
    ...
}