MCP server liveness

whether the server asked for authorization (401, 403 or a WWW-Authenticate header — such a server can be healthy; it is not probed further), the protocol version it answered with, how many tools tools/list returned (only when initialize succeeded without authorization), the time from the first request to the answer to initialize or to the failure (latency_ms), the kind of failure (error_class: dns, refused, reset, unreachable, tls, timeout, private-address, redirect, http-4xx, http-5xx, not-sse, bad-response, jsonrpc-error, too-large, auth, or tools-list-… when only the tool listing failed), when, and the vantage. Method: every endpoint of type streamable-http or sse of every server at its latest version in the registry (template URLs left out) is sorted and at most 500 are probed a day, a different slice each day, so the list is covered over several days; 8 at a time, 10 s per step, one attempt, no retry. streamable-http: POST initialize (protocol version 2025-11-25), then notifications/initialized and tools/list, then the session is closed. sse: the stream is opened, initialize is posted to the endpoint it names (same host only) and the answer read from the stream. No tool is ever called, no credential or cookie is sent, redirects are not followed (recorded as redirect), and hosts that resolve to private, loopback or link-local addresses are not contacted. Vantage bias: one server, one shared AWS EC2 host in Seoul (ap-northeast-2), the host WITAN's worker runs on — its network, region and provider shape latency and reachability; an endpoint that is unreachable from here may be fine elsewhere, and a single failed probe is not an outage. Attribution: the source list is the Official MCP Registry (registry.modelcontextprotocol.io), read through WITAN's mcp-registry-snapshot dataset, whose data the registry dedicates to the public domain under CC0 1.0; the measurements are WITAN's own. WITAN is not affiliated with or endorsed by the registry or the servers measured, and a record is not an endorsement. Opt-out: the operator of a server that does not want it probed or listed here can ask through the contact address on https://witan.markets/terms#takedown (or https://witan.markets/report); its host or server name is taken off the probe list (a setting, no code change), so no new records are made; published versions are immutable, so the records already in them stay, and the opt-out is noted here. Free: public and free to pull with an agent key. License: the WITAN Standard License covers this dataset — every value in it is WITAN's own measurement; the server names and hosts come from the registry (CC0 1.0).