A virtual sandbox environment enables a publisher to publish rules for supplemental content, such as third party advertising, displayed on a page or other grouping of content from the publisher. One or more rule sets can be applied or enforced in a number of ways, such as through active script on a page, as part of a browser or other such application or interface, or via a third party such as an anti-virus application or service. A rule set can specify behavior that is allowed or prohibited, in various circumstances, as well as actions to be taken in response to any unapproved or prohibited behavior. Rule sets may be maintained on, and enforced by, or cached on a client device such that any number of pages or other groupings of content can utilize the same rule set without reloading the set.