Rate Limiting for Yahoo! Search Web Services

This document describes how rate limits apply to our Web Services. The limits for each service are independent and are described in the per-service documentation.

Understanding Rate Limiting

IP Based Limits

Our service rate limits are imposed as a limit on the number of API calls made per IP address during a specific time window. If your IP address changes during that time period, you may find yourself with more "credit" available. However, if someone else had been using the address and hit the limit, you'll need to wait until the end of the time period to be allowed to make more API calls.

24 Hour Period

The service limits are expressed in API calls per 24 hour period. You can think of this as a day, however the clock does not reset itself at midnight. Instead, we begin counting the first time we see an API call from the IP. Then 24 hours later, we reset the counters for your IP address.

Rate Limiting Graph

The figure above illustrates this behavior. In the first example, User A's usage remains below the limit for the duration of each day, so his requests are always served. In the second example User B hits the limit before the 24 hour period is over and is blocked from making additional requests until the counters are reset at the end of each day.

When you hit the limit...

When you exceed the specified limit for any given service, you'll receive the following XML response to any API call: