Wikipedia:Quick and dirty Checkuser policy

The community can grant administrators the permission to use the m:CheckUser interface solely for the purposes of tracing the source of persistent vandalism by showing consensus in favour with an WP:RfA-like vote. Any users granted the CheckUser right in this way may not use the checkuser privilege for anything other than tracing the source of persistent vandalism unless further policy on the matter allowing to use it for other purposes is created.

The CheckUser facility may also be used for investigating matters of interest to the Arbitration Committee at an arbitrator's request.

You can see how CheckUser works at meta:Help:CheckUser.

The original proposal can be found at /proposal.