From How API Keys Work (FAQ) I read that the limit of requests per day per IP is 300 without a registered key, or 10000 with it.
And this is what I see by experimenting myself: since I've not registered any key yet,
300 for me (well, it was, before I emptied the
quota_remaining thus running into the
too many requests from this IP error which banned me out for more than 5 hours from now), just like explained in this answer.
However, in the Throttles documentation I see that
quota_remaningis mentioned, so I'm inclined to think the page is about the same topic as the FAQ linked above,
- but no
300limit is mentioned;
- instead, the limit of
10000is stated whether or not "the application" has an "access_token",
- the same
10000limit the FAQ linked above associates to the requests made with the key.
As a further observation How API Keys Work (FAQ), which mention
300 as a limit, also links directly to throttles,
These limits are per user IP address, per-day, with some exceptions.
which doesn't mention
300 as a limit. I guess this is at least an inaccuracy in the doc?