Active URIs are a syntax of Universal Resource Identifier (URI) which was designed especially for NetKernel to a service interface with an arbitrary number of named arguments which are themselves nested URIs. In the general case this leads to its unique ability to specify complete functional programs within it's syntax.

Hewlett Packard and 1060 Research embarked upon a standardisation of the Active URI with the IEFT in 2003 but that attempt has since stalled. A draft of the specification is available here.

In summary the syntax of the active URI is:

"active:" {service-name} [ "+" {argument-name} "@" {argument-value } ]*