How reliably endpoints answer, over time rather than at one instant.

/state-of-mcp says what share of the index answers right now. This says what share of probes an endpoint has answered, which is the question a consumer actually has, and it is only answerable by something that has been probing on a timer and counting.

Rates are withheld below a minimum number of probes. A single successful probe is not 100% uptime, and publishing it as one would be the most quotable wrong number on the site.