Question 1

What is JSON and what does it stand for?

Accepted Answer

JSON (JavaScript Object Notation) is a lightweight, text-based data interchange format. Despite its name, JSON is language-independent and supported by virtually every programming language. It was derived from JavaScript's object literal syntax but is now standardized as ECMA-404 and RFC 8259. JSON represents data as key-value pairs (objects) and ordered lists (arrays) using a simple, human-readable syntax.

Question 2

What is the difference between JSON and XML?

Accepted Answer

JSON and XML are both data interchange formats, but JSON is more compact and easier to read. JSON uses key-value pairs and arrays, while XML uses nested tags. JSON is natively parsed by JavaScript (JSON.parse()), while XML requires a DOM parser. JSON doesn't support comments, XML does. JSON is the dominant format for web APIs, while XML is still used in enterprise systems, SOAP services, and configuration files (like Android layouts and Maven).

Question 3

How do I validate JSON?

Accepted Answer

JSON is valid if it follows the ECMA-404 specification: objects use curly braces with quoted key-value pairs, arrays use square brackets, strings must use double quotes (not single quotes), no trailing commas are allowed, and no comments are permitted. Use JSON.parse() in JavaScript (it throws SyntaxError for invalid JSON) or an online validator like this tool. Common errors include trailing commas, single quotes, unquoted keys, and comments.

Question 4

What is JSON Schema and how is it used?

Accepted Answer

JSON Schema is a vocabulary that allows you to validate the structure of JSON data. It defines the expected data types, required fields, value constraints (min, max, pattern), and nested object structures. JSON Schema is written in JSON itself and is used for API request/response validation, form generation, configuration file validation, and documentation. It's similar in purpose to XML Schema (XSD) but for JSON.

Question 5

What is the difference between JSON.stringify() and JSON.parse()?

Accepted Answer

JSON.stringify() converts a JavaScript object/value into a JSON string (serialization). JSON.parse() converts a JSON string back into a JavaScript object/value (deserialization). JSON.stringify() accepts optional replacer and space arguments for filtering and formatting. JSON.parse() accepts an optional reviver function for transforming values during parsing.

Question 6

What is pretty-printing JSON and why is it useful?

Accepted Answer

Pretty-printing (or formatting) JSON adds indentation and line breaks to make the data human-readable. Minified JSON like {"name":"John","age":30} becomes formatted with proper indentation. Pretty-printing is essential for debugging, code review, documentation, and manual inspection. It doesn't change the data — only the whitespace. Our tool formats JSON with configurable indentation (2 or 4 spaces).

Question 7

What are common JSON data types?

Accepted Answer

JSON supports six data types: (1) String — double-quoted text ("hello"). (2) Number — integer or floating-point (42, 3.14, -1, 2.5e10). (3) Boolean — true or false (no quotes). (4) null — represents no value. (5) Object — unordered collection of key-value pairs in curly braces. (6) Array — ordered list of values in square brackets. JSON does NOT support undefined, functions, dates, or comments.

Question 8

Why does JSON require double quotes for keys and strings?

Accepted Answer

The JSON specification (RFC 8259) mandates double quotes for all strings and object keys. This was a deliberate design choice for simplicity and unambiguity — single quotes, unquoted keys, and template literals are JavaScript features that don't exist in JSON. This strict syntax makes JSON parsers simpler and more interoperable across languages. Using single quotes or unquoted keys is the most common validation error.

Question 9

What is JSONL (JSON Lines) and how does it differ from JSON?

Accepted Answer

JSONL (JSON Lines, also called NDJSON — Newline Delimited JSON) is a format where each line is a valid JSON value, typically a JSON object. Unlike a JSON array, JSONL can be processed line by line without parsing the entire file, making it ideal for log files, streaming data, and large datasets. Example: {"name":"Alice"}
{"name":"Bob"}. Many data processing tools (jq, pandas, BigQuery) support JSONL natively.

Question 10

How do I handle JSON in different programming languages?

Accepted Answer

JavaScript: JSON.parse() / JSON.stringify(). Python: import json; json.loads() / json.dumps(). Java: Use Gson, Jackson, or org.json libraries. C#: System.Text.Json or Newtonsoft.Json. Go: encoding/json with Marshal/Unmarshal. Ruby: require 'json'; JSON.parse / JSON.generate. PHP: json_decode() / json_encode(). Rust: serde_json crate. Every modern language has built-in or standard library JSON support.

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