Complete RFC 8259 JSON Specification & Grammar Reference

JSON (JavaScript Object Notation) is governed by IETF RFC 8259 and ECMA-404. It is a lightweight, text-based, language-independent data interchange format.

1. Core Data Types in RFC 8259

RFC 8259 defines six fundamental primitive and structural data types:

Objects ({ }): Unordered collections of zero or more key-value pairs. Keys MUST be double-quoted strings.
Arrays ([ ]): Ordered sequences of zero or more values of any type.
Strings ("..."): Sequences of Unicode code points enclosed in double quotes ("...).
Numbers: Signed decimal numbers in standard or scientific exponential notation.
Booleans: Keyword literals true or false (strictly lowercase).
Null: The keyword literal null.

{
  "name": "JSON2X Enterprise API",
  "version": 2.4,
  "isActive": true,
  "metadata": null,
  "tags": ["developer", "tools", "privacy-first"]
}

2. String Escaping & Special Characters

RFC 8259 mandates backslash (\) escaping for special control characters:

Character	Escape Sequence	Description
Quotation mark	`\"`	Double quote character
Reverse solidus	`\\`	Backslash character
Solidus	`\/`	Forward slash (optional)
Backspace	`\b`	Backspace control code
Form feed	`\f`	Form feed control code
Line feed	`\n`	Standard Unix newline
Carriage return	`\r`	Carriage return
Tab	`\t`	Horizontal tab
Unicode code point	`\uXXXX`	4-hex digit Unicode hex

3. Strict RFC 8259 Parsing Rules

No Single Quotes: Keys and string values must strictly use double quotes ("key": "value").
No Trailing Commas: A comma after the final element in an object or array causes a syntax violation.
No Unquoted Keys: Property names like { age: 30 } are valid JavaScript object literals, but invalid JSON.
No Comments: Comments (// or / /) are prohibited under standard RFC 8259.
No Leading Zeros: Numbers like 0123 or +42 are invalid in JSON.

4. Frequently Asked Questions

Why does JSON reject single quotes?

RFC 8259 explicitly standardized on double quotes (") to ensure absolute cross-platform interoperability across all programming language parsers (C, Java, Python, Go, Rust).

How does client-side validation prevent data corruption?

Client-side validation runs in the browser's JavaScript engine before network transmission, preventing invalid payloads from hitting backend databases and APIs.

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