Jakarta Pluto is the Reference Implementation of the Java Portlet Specification. The current version of this Portlet specification is JSR 168 1.0 Portlets are designed to run in the context of a portal. They are written to the Portlet API. Pluto implements the contract, the Portlet API, between portlets and portals. Pluto is a portlet container.

A portlet container provides a runtime environment for portlets implemented according to the Portlet API. In this environment portlets can be instantiated, used and finally destroyed. The portlet container is not a stand-alone container like the servlet container; instead it is implemented as a thin layer on top of the servlet container and reuses the functionality provided by the servlet container.

Pluto serves as portlet container that implements the Portlet API and offers developers a working example platform from which they can test their portlets. However, it's cumbersome to execute and test the portlet container without a driver, in this case, the portal. Pluto's simple portal component is built only on the portlet container's and the JSR 168's requirements.