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Overview

Caspen applies a single throttle: 60 requests per minute for each API key. The throttle window starts when you make the first request and resets 60 seconds later, at which point the allowance refills to 60 calls.

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Current limit

Limit typeRequestsWindowScope
Standard6060 secondsPer API key

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Reset behavior

When you send a request, the counter tracks how many calls you have made in the last 60 seconds. Once a call becomes older than 60 seconds, it no longer counts against the quota. There is no separate daily or monthly limit.

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Response headers

Every response includes throttling headers so you can monitor usage: 
HTTP/1.1 200 OK
X-RateLimit-Limit: 60
X-RateLimit-Remaining: 1
HeaderDescription
X-RateLimit-LimitMaximum requests allowed in the rolling window (always 60).
X-RateLimit-RemainingRemaining requests before you hit the limit.
Retry-AfterSeconds to wait before retrying. Only present when you are limited.
X-RateLimit-ResetUnix timestamp for when the current window resets.

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When you exceed the limit

If you send more than 60 requests within 60 seconds, Caspen returns 429 Too Many Requests with a short error body and backoff headers. 
HTTP/1.1 429 Too Many Requests
X-RateLimit-Limit: 60
X-RateLimit-Remaining: 0
Retry-After: 32
X-RateLimit-Reset: 1758868775
Content-Type: application/json

{"message":"Too Many Attempts."}
Wait for the number of seconds indicated in Retry-After or until the time reported in X-RateLimit-Reset before sending the next request.