The official API documentation is here in the Node-RED docs.
The API is accessed via the
Available in Function Nodes 🔗︎
Available in Custom Nodes 🔗︎
See: https://groups.google.com/forum/#!searchin/node-red/RED.util/node-red/dOrpj2S_hi0/X0LthFt0BAAJ “For a variety of reasons, you cannot use the JSON.stringfy/parse trick on messages that originate from the HTTP In node.”