AWS customer Capital One has released a new open source tool that helps organizations define policies around cloud usage.

Called Cloud Custodian, the tool is a rules engine that Capital One has used internally to reduce AWS resources by 25 percent, according to a report by TechCrunch.

The announcement was made this week at AWS Summit in Chicago where AWS made a number of releases and updates.

Cloud Custodian uses CloudWatch Events, which AWS released in January to provide an efficient way to monitor events. The tool also leverages the Lambda service, announced at last year’s re:Invent conference, which can launch a set of resources for a given set of rules for a set period of time, according to TechCrunch.

By using Cloud Custodian, AWS customers can monitor resources and turn off instances when they aren’t being used. The result is a cost-savings that could be fairly significant depending on the number of instances in use.

Cloud Custodian is available on Github.

Netflix is another AWS customer that has released open source tools developed internally for managing its AWS own cloud infrastructure, including a tool it developed to monitor security threats.