@nala it is possible/reasonable to do that. Most projects I've seen have used

api

in conjunction with spring security rest to make APIs available to third parties, although it doesn't necessarily have to be that way. In Grails 2.x you can just do a

render something as JSON

instead of a respond. Although those converters are deprecated once you get to Grails 3 or beyond, and instead you have JSON views which are similar to GSPs but for JSON. It's also worth noting that Grails 4 and below are EOL, and will get no updates. Upgrading from 2.x to anything above can be changing depending on how big your code base is and how many practices you have that are considered bad and no longer supported. After upgrading beyond 2.x, subsequent updates are a lot easier.