Rate limits

<!-- order: 6 | How many requests a minute, and how to stay within them. -->

Caller	Requests a minute
No key (the public catalog), per address	60
A person (explorer or personal token)	300
An organization's key	600

Every response says where you are:

RateLimit-Limit: 600
RateLimit-Remaining: 597
RateLimit-Reset: 41

Over the limit, you get 429 rate_limited with retry_after. Wait that many seconds and carry on. For a whole copy of the catalog, use /v2/catalog/export once and then the change feed, rather than paging through everything often.