JSON

JSON is how two programs pass structured data without sharing a language.

JavaScript Object Notation. Curly braces. Quoted keys. Values that are strings, numbers, booleans, lists, or more objects. No comments. That last part is on purpose. The file is a payload, not an essay.

{ "title": "Buy milk", "done": false }

Your REST API speaks this on the wire. So does almost every vendor. So does the clipboard when an agent says "here's the data." A Python service can hand this to your TypeScript frontend and both sides parse it.

The schema is the blank. JSON is one filled answer.

The schema says which keys exist and what type they are. JSON is the actual object. If a key is missing or a number is a string, the parse should fail before you write the database.

You will see it everywhere the builder touches: request bodies, responses, package.json, the Polar event. Learn to read the braces as a labeled list. You are not looking at code. You are looking at a bag of fields.

YAML can hold the same facts. Put JSON on the wire. Put YAML in the config a human has to edit. Do not convert by eye at 4 a.m. Use a tool. And never drop a secret into a JSON blob you then commit "as fixture data."

What this unlocks

Once you can read a JSON body, the Network tab stops being a blur.

The API is not magic. It is this object, going in, coming back.