Hi Friedrich

in the MagritteMagicExample (which seems to be the only Example
available for Magritt3 one can find:
talkJson: talkTitle
       <produces: 'application/json'>
       <path: '/talk?title={talkTitle}'>

       | talk |
       talk := self talkFromTitle: talkTitle.
       self requestContext respond: [ :response |
                       contentType: WAMimeType applicationJson;
                       nextPutAll:  talk asJson ]

So it seems this should produce come Json format. Does that work for

If you load Magritte Magic using the Metacello configuration it will also load Magritte-Json and Magritte-XMLBindings found in http://source.lukas-renggli.ch/magritte3addons

They will Magritte described objects to serialise or materialise in Json or XML format.

Another example of Magritte 3 is in the Magritte examples in: http://twitterbootstrap.seasidehosting.st/