JSON: the text all network APIs speak

TL;DR

JSON is a text format for structured data: objects with key–value pairs, ordered arrays and six value types (object, array, string, number, boolean, null), defined in RFC 8259. The syntax is strict: double quotes, no comments, no trailing comma, decimal numbers; any deviation means 400 Bad Request at an API. In networking you meet it in the body of the HTTP messages of REST APIs, in RESTCONF (where its shape is dictated by the YANG models, per RFC 7951), in Python (dict ↔ object via json.loads / json.dumps), on NX-OS with | json, in the Catalyst Center and Meraki APIs, in Ansible (register, inventory, -e) and in the shell with jq. Most incidents come from syntax, from the forgotten module prefix, from wrongly assumed types (string instead of number, object instead of array) and from JSON built by concatenation; the serializer, the schema and reading the error body fix them all.

How to read the notes: red = critical for the exam, green = theory, blue = numbers, yellow = pitfalls, cyan = differences between platforms, languages and standards. In the animations, the configuration lines used at the current step are highlighted automatically; the ← → arrows change the step when the animation is focused.