What is JSON?

Why this matters

JSON is the de facto standard for exchanging data between web APIs, config files, and applications — understanding its structure makes debugging, editing config, and reading API responses far easier.

Definition

JSON represents data as nested key-value pairs (objects, written with `{}`) and ordered lists (arrays, written with `[]`), built from six value types: string, number, boolean, null, object, and array. It was derived from JavaScript object literal syntax but is language-independent — nearly every programming language has a JSON parser.

How it works

A JSON document is plain text. A parser reads that text and converts it into the equivalent native data structure in whatever programming language is being used — for example, a JSON object becomes a Python dict or a JavaScript object. The reverse process, turning a data structure back into JSON text, is called serialization.

Step by step

1. 1Data exists in a program. A structure like a list of user records lives in memory as native objects.
2. 2Serialize to JSON. The program converts that structure to a JSON text string, e.g. to send in an API response.
3. 3Transmit or store. The JSON text is sent over the network, saved to a file, or stored in a database.
4. 4Parse back. The receiving program parses the JSON text back into a native data structure it can work with.

Common mistakes

• Using single quotes instead of double quotes around strings and keys — JSON requires double quotes.
• Leaving a trailing comma after the last item in an object or array — this is valid in JavaScript but invalid JSON.
• Adding comments — JSON has no comment syntax, unlike JavaScript or JSON5.

Best practices

• Validate JSON before using it in production, especially if it's hand-written or comes from an untrusted source.
• Keep keys consistently named (e.g. always camelCase or always snake_case) across a document.
• Use a formatter to keep deeply nested JSON readable during development.

Related guides

• JSON formatting vs. minification: what's the difference?
• What is Base64 encoding?

Sources

• RFC 8259 — The JavaScript Object Notation (JSON) Data Interchange Format
• ECMA-404 — The JSON Data Interchange Syntax