Should a front-end developer ever specify JSON format for back-end developers

At jClarity we've definitely followed this approach. We have a 'pure' HTML5 front end - AngularJS, HTML, CSS and a host of Javascript micro frameworks which is a separate project to the backend - vert.x with a variety of verticles coded in separate JVM languages as appropriate.

The trick is to have a well defined messaging API between the two that is tested by JUnit/TestNG style integration tests (backend) and Jasmine/Selenium tests (front end).

It's worked really well for us, great separation of concerns with the only dependency being on the messaging API between the front end and back end. We use a bit of clever Maven magic to check that the dependencies are correct between the two as well as end to end tests.

Despite an upfront cost in getting this all set-up, I've been amazed to see how quickly new functionality can be added with confidence using this structured approach. Even better, there's no stinking UI/View logic in our server side code and visa versa.

So in short - I highly recommend it :-).

Coming from a front-end developer perspective, I prefer simple and semantic as much as possible. Generally inside a consistent envelope for debugging and tracking, the actual data would be as follows:

{
    "images" : [
        {
          "id" : 123,
          "filename" : "someFile.jpg",
          "caption" : "some image or other",
          "gallery" : 123
        },{
          "id" : 124,
          "filename" : "someFile.jpg",
          "caption" : "some image or other",
          "gallery" : 124
        }
    ]
}

Envelopes often look something like this:

   {      
      "messageID"     : "sflskdfj-asldkja-asdlk", // some uuid
      "sendDate"      : 1394134506764, // time at which the server sent the message
      "requestMethod" : "GET",
      // whatever else you want for front-end tracking or debugging
      "data"          : {
          "images" : [...]
      }
   }