Aalto XML processor is an ultra-high performance next generation Stax XML processor implementation, implementing both basic Stax API (javax.xml.stream) and Stax2 API extension (org.codehaus.woodstox.stax2). In addition, it also implements SAX2 API.

In additional to standard Java XML interfaces, one unique feature not implemented by any other Java XML parser that we are aware is so-called non-blocking (asynchronous) XML parsing: ability to parse XML without using blocking I/O, necessary for fully asynchronous processing such as those with Akka framework. Aalto non-blocking API is a minimalistic extension above Stax/Stax2 API to allow indication of "not yet available" token (EVENT_INCOMPLETE) as well as feeding of input (since InputStream can not be used as it blocks).