...
For the benefit of all users of the Europeana APIs, it is imperative that users adhere to fair and reasonable use of each API to seek to prevent downtime, loss of or corruption or damage to data and/or other errors or technical issues that may result for from excessive use of the API.
Use of the API must be limited to a reasonable number of concurrent calls (API requests), together with an appropriate wait period for completion of those calls before commencing further calls. We may specify a specific number of call limits from time to time, to which you will be required to adhere.
In the event that you receive error reports or error codes from use of our API you must immediately notify us, and reduce your usage of the API appropriately.
Keys: The API may require a key to run or access. You are responsible for and liable for the installation and use of keys and must not copy or share the keys with third parties.
...