API throttling and rate limits

Overview

Canada Post has set API throttling and rate limits that should be sufficient for almost all reasonable business cases. However, the limits are different for each product (Rating, Shipping, Tracking, and so on) based on their expected usage.  

Please note: Limits for the test API environment may be set lower than for the production environment.

Avoiding rate limits

Throttling limits are enforced in a rolling 60-second window. If you exceed this limit, you’ll be blocked from making further API calls until the current 60-second window expires. This rolling window isn’t tied to any standard time. The best way to ensure you won’t trigger the limit is to place delays of at least 250 milliseconds between each API call.

If you exceed the rate limit

You’ll get the following error when the throttle limit is exceeded:

Server	Rejected by SLM Monitor 

If you get this error, wait 60 seconds and then retry your request.