Google books API and the neccesity of an API key

Question

So Google claims that in order to use their Google Books Api, you have to register and get an API key. But you can make a request without an api key.

e.g.:

https://www.googleapis.com/books/v1/volumes?q=isbn:9780553819229

Why would I register if I can make requests without a key? I don't get it.

Answer 1

Along with the Terms of Use mentioned by Will, the biggest reason is that when you use an API key, the API request isn't throttled as much.

You'll get the following error much quicker without using the API key:

{
 "error": {
  "errors": [
   {
    "domain": "usageLimits",
    "reason": "userRateLimitExceededUnreg",
    "message": "User Rate Limit Exceeded. Please sign up",
    "extendedHelp": "https://code.google.com/apis/console"
   }
  ],
  "code": 403,
  "message": "User Rate Limit Exceeded. Please sign up"
 }
}