In order to ensure API stability, HCSS APIs enforce rate limits on client applications. More specifically, we count requests from applications, and if the total count exceeds the limit for a specified period of time, API access for your application will be throttled. That is, HCSS APIs will return HTTP 429 Too Many Requests until your application is under the rate limit.
We do not publish what the actual limits are; however, their intent is to prevent accidental denial-of-service attacks from a misconfigured application. If your application is getting rate-limited through its normal course of operation, please contact us at firstname.lastname@example.org.