Network state, mining difficulty and hashrate. Mining pull distribution. Information about nodes, unconfirmed transactions and unconfirmed pool statistics. Reasonable transaction fee rate, calculated from last blocks and mempool state.
For API, restrictions of requests by IP addresses apply. Standard limit 15 requests within 5 seconds for a single IP address. If you need more requests, then you need to purchase an API token. For questions about obtaining a token API, contact firstname.lastname@example.org. If the limit is exceeded, a page with the status 429 to many requests is given in response to the request. If an error is received, you should wait for the time limit to be restored, otherwise the IP address will be blocked for 3 minutes. The current status of the limits can be found in the response headers Ratelimit-Remaining and Ratelimit-Reset .