Rate Limits
Key-gated endpoints are rate-limited per API key by your plan, with both a per-minute and a per-month budget. Every response carries quota headers, and exceeding a limit returns 429 with Retry-After.
Per-key limits
Limits are enforced per API key, so multiple keys on one account each get their own budget. The minute window smooths bursts; the monthly window caps total volume.
Quota headers
Every key-gated response includes headers for both windows, so you can throttle proactively instead of waiting for a 429:
Handling 429
When you exceed either window the API returns 429 Too Many Requests with a Retry-After header (seconds to wait). Back off for that long, then retry, preferably with exponential backoff and jitter for bursts. Cache where you can: the NBBO and pricing feeds are meant to be polled at a steady cadence, not hammered.
Market Health
Market health, the one keyless endpoint, is limited separately by IP (roughly 60 requests / 60s) and returns no per-key quota headers. Every other endpoint is key-gated; see Authentication to get a key.