Which endpoints answer, as a feed anyone may consume, including rivals.

We probe every endpoint we index and keep the transitions. Other registries do not, which means they list servers that stopped answering months ago and have no way to know. Publishing this costs us nothing we would otherwise sell and makes the whole ecosystem less wrong, which is worth more to us than the small advantage of being the only ones who can tell.

No key, no attribution required, no rate limit beyond the shared one. dead=1 is the useful half: the entries worth re-checking on your side.