Configuring with a JSON file helps avoid manually typing in workflow inputs and outputs and can get your WDL up and running in record time. This is especially useful when you want to quickly test that a WDL workflow can run successfully on Terra without setting up a workspace data table.
 

Uploading a JSON file of inputs to populate the workflow configuration

You can find the link to upload or download a JSON on the form that appears when you click a workflow card: 

JSON is the format most commonly used to specify inputs for a WDL workflow outside of Terra, so this is especially useful if your workflow was developed and tested on a different platform and already comes with a JSON file of inputs. For example, this feature makes it easy for you to run a WDL from Dockstore if it is accompanied by a JSON file, as is usually the case (see the Test file section in the Dockstore repository of interest). Note that if you are trying to use a WDL with a JSON file that was tailored for a different platform, you'll need to make sure you update the paths to any files to point to locations in Google Cloud storage that FireCloud can access.

Downloading a JSON file to copy and re-use lists of input files and parameters

You can download your JSON file in the same way, which comes in handy when you want to use the same inputs across workflow configurations. For example, if you create a new configuration, normally you’d have to enter all of the inputs manually every time, even if this new configuration will use many of the same inputs as an existing one. Now you can download the inputs from the prior configuration as a JSON and upload that to populate the new configuration.

Admittedly it would be even better to be able to copy inputs from one configuration to the other within Terra itself - and we're looking at ways to make that happen in the future - but at least the ability to save inputs to file and re-upload is a big step up from having to fill out each field one by one manually! Right?