    info {
        domain adguard.com
        type unfiltered
        protocol auto
        addr 176.103.130.136 176.103.130.137
        canary dnscheck.adguard.com
    }

Discovery requests look like: *-{protocol}-{type}-dnscheck.{domain}. For instance, 12321-doh-unfiltered-dnscheck.adguard.com. If the domain is queried using doh protocol from a server with type unfiltered, the request will return the specified addr. Otherwise, it will return NXDOMAIN.

domain - registered domain that will be used in the discovery DNS queries.
type - server type (any string).
protocol - possible values are dns, doh, dot, dnscrypt, auto.

If it's set to auto, the plugin will try to detect the protocol by itself. If it's set to a specific protocol, the plugin won't try to detect anything.
addr - the list of addresses to return in the discovery response. You can specify multiple addresses here. IPv4 addresses will be used for A responses, IPv6 - for AAAA.
canary - (optional) simple "canary" domain which only purpose is to test whether AdGuard DNS is enabled or not without any additional logic (protocol or type detection) on top of it.

Note: canary domain is used by third-party services that may want to discover if AdGuard DNS is used or not. For instance, Keenetic routers use it.