Hello Linda,
there is, to my knowledge, no industry standard, however there are some suggestions and best practices on what should be monitored on APIs.
In a nutshell, it suggests the following metrics:
- Request volume
- 2xx/3xx/4xx/5xx rates
- Server load
- Error log rate
To quote the procedure from the article: "Once you’ve identified these norms and an acceptable range around them, you can then set up alerting for when they are exceeded. This can be as simple as a threshold (we’re over 2% 400/500 rate = alert) to more complicated setups (we’re seeing a larger-than-normal request volume from IP address X over the past 10 mins — is this DDoS?).“
Hope this gave you some hint on how to monitor API performance.
Regards,