What is JSON?

JSON is just a (usually long) string whose contents follow a specific format.

One example of JSON:

{
    "key": "value",
    "another": 25,
    "listic_data": [
        1,
        3,
        7
    ],
    "sub_objects": {
        "name": "Rolf",
        "age": 25
    }
}

So at its core, you've got:

• Strings
• Numbers
• Booleans (true or false)
• Lists
• Objects (akin to dictionaries in Python)
• Note that objects are not ordered, so the keys could come back in any order. This is not a problem!

At the top level of a piece of JSON you can have an object or a list. So this is also valid JSON:

[
    {
        "name": "Rolf",
        "age": 25
    },
    {
        "name": "Anne",
        "age": 27
    },
    {
        "name": "Adam",
        "age": 23
    }
]

When we return a Python dictionary in a Flask route, Flask automatically turns it into JSON for us, so we don't have to.

Remember that "turning it into JSON" means two things:

1. Change Python keywords and values so they match the JSON standard (e.g. True to true).
2. Turn the whole thing into a single string that our API can return.

!!! tip JSON looks different? Note that JSON can be "prettified" (as the above examples), although usually it is returned by our API "not-prettified":

json [{"name":"Rolf","age":25},{"name":"Anne","age":27},{"name":"Adam","age":23}]

This removal of newlines and spaces, believe it or not, adds up and can save a lot of bandwidth since there is less data to transfer between the API server and the client.