There are tons of emails that share the same prefix. When you lookup a prefix, you can't simply get a boolean response. You have to get a list of emails as the response. The client then searches through the list to see if the desired email is in the list or not. Returning a list of emails instead of a single bit significantly increases the data size.

Additionally, people don't just want a boolean answer of "was my email breached somewhere". They want a list of all the breaches that breached the email. So the returned data actually needs to be a list of emails and the list of breaches that each email was breached in.

>Via the public API. This endpoint also takes an email address as input and then returns all breaches it appears in.