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Every answer says how fresh it is. A source that is dead, absent or older than its bound answers 503 upstream_unavailable (or dependency_unavailable for our own stores), never an empty 200. The bounds shown are the API’s configured values. Notes:
  • An order book’s ts_ms is its last change, so a quiet live book can be old.
  • A Limitless book is also checked against the venue as a whole. Our market-data feed records, once a minute, how many Limitless updates it received live and applied. When that record shows none in the last 120 s (an environment setting), or the record is missing or unreadable, every Limitless book answers 503 upstream_unavailable, however recent its own ts_ms, because the Limitless feed may have stopped. If our own store cannot be read for this check, the answer is 503 dependency_unavailable. Books are served again once the record shows Limitless updates; we check about every 15 s. Other venues are not checked this way.
  • A trade tape is written only on a trade, so a quiet market’s tape can be days old.
  • A Limitless trade can reach us about a minute after it happened (an estimate from one observed trade), so the newest Limitless trades may be missing for that long. The Limitless check above applies to books only, not to trades.
  • A candle series’ last_bar_ts_ms is information, not a liveness signal: a quiet market adds no bars.
  • In a price snapshot, closed_gate says whether the closed-leg check ran; when it reads unavailable, an absent closed does not mean none is closed.