There exist multiple tools to aid you with writing decoders:

- json-to-elm http://json2elm.com

- swagger-elm https://github.com/ahultgren/swagger-elm/

- elm-graphql https://github.com/jahewson/elm-graphql, https://github.com/jamesmacaulay/elm-graphql

- elm-export https://hackage.haskell.org/package/elm-export

Once you've got the hang of it, it's not that hard either. Just time consuming. That's where json2elm comes in :)

Once you handle a couple of complicated cases, you're ready to solve any JSON decoding within minutes. It's just a small learning curve to go through.

Also, once you get the hang of it, you can use it as your safety layer for incoming data. To guard the app from any invalid response.

I've even used GraphQL for one of my projects, decoding worked fine as well.