Endpoint health
Every documented operation is called against the production API on a schedule and the answer is held against this reference: the status, the media type, the schema, the fields promised against the fields sent, the cache contract, and who may call it. This is the last run, in full, failures included.
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Whether the API is answering at all is a different question, and the status page answers it: a deploy serving last week's contract is perfectly available and wrong. The printed examples are checked too.