Is there a limit on the number of requests we send to the API?
We employ multiple algorithms to protect the operational integrity of our API, ranging from simple rate limits to dynamic systems which take into account the CPU time consumed across all of our backend services by each request and the total capacity available to serve them. If you are rate-limited in any way you will receive a 429 status code, at which point your client application should respond with exponential backoff or a similar throttling measure. In general these limits are high enough that non-abusive request patterns will not trigger them.
We provide "batch" APIs for many operations, including shipment and tracker creation. If you are regularly encountering our rate limiters, we recommend that you move to an asynchronous/batch workflow.