Freebase has a sibling called Sandbox (sandbox.freebase.com). This site is mostly identical and is intended to be used as an area for experimentation. For instance, if you are planning to do a large data load, it is generally recommended that it be tested on Sandbox first.

The data on Freebase is copied over to Sandbox once a week (typically on Monday afternoons). At this time, any accounts that have been added to Freebase in the previous week will also be copied over - and the same login information that works on Freebase will subsequently work on Sandbox.

Edits are wiped away on Mondays!

This also means that any data that you have loaded to Sandbox will be overwritten at this time. This is done so that people can experiment with a recent copy of the Freebase data set. It also provides some freedom if people submit damaging changes or changes they don't intend to keep, this is all cleaned up automatically for them.

In the future, we plan to have utilities that will allow you to mark selected content for preservation. In the meantime, if you are creating types that you'd like to retain, we recommend creating them in your private domain on Freebase, not on Sandbox.