As stated in the Selenium Builder wiki under Data driven Testing you can store variables as an array of objects.
For your use you will make the file look like this:
[
{"url" : "https://my_url"}
]
save the file as test_values.json in the same folder as your test and reference it like this in your test.json:
"data": {
"configs": {
"json": {
"path": "test_values.json"
}
},
"source": "json"
},
If you need to pass multiple variables to your test do it inside the object (the curly braces) like this:
[
{
"url" : "https://my_url",
"user" : "some_user",
"password" : "some_password"
}
]
Now, the fun part is, that if you add another object (set of curly braces) like this:
[
{
"url" : "https://my_url",
"user" : "some_user",
"password" : "some_password"
},
{
"url" : "https://my_url",
"user" : "some_other_user",
"password" : "some_other_password"
}
]
Then the test will run twice. Once with the first set of values, and the second time with the second set of values.