RFC 8259: The Official JSON Specification Guide

RFC 8259: The JSON Standard

RFC 8259 (published December 2017) is the authoritative IETF Internet Standard for the JSON data interchange format. It is co-published with ISO/IEC 21778:2017 and technically equivalent to ECMA-404.

Key Requirements of RFC 8259

1. Encoding: JSON text MUST be UTF-8 encoded.
2. Double quotes only: String values and object keys must use double quotes (").
3. No comments: JSON does not define any comment syntax.
4. No trailing commas: A comma after the last element in an object or array is illegal.
5. No leading zeros: Numbers like 0123 are invalid.
6. No NaN or Infinity: These IEEE 754 values have no JSON representation.
7. Lowercase literals: true, false, and null must be lowercase.

RFC 8259 History

• RFC 4627 (2006) — Original JSON specification by Douglas Crockford.
• RFC 7159 (2014) — First revision, clarified interoperability.
• RFC 8259 (2017) — Current standard, mandates UTF-8.

// RFC 8259 Compliance Examples

// ✅ Valid RFC 8259 JSON:
{
  "name": "Alice",
  "age": 30,
  "active": true,
  "data": null,
  "roles": ["admin", "editor"]
}

// ❌ Invalid under RFC 8259:
{
  'name': 'Alice',     // ❌ Single quotes
  age: 30,             // ❌ Unquoted key
  "items": [1, 2,],   // ❌ Trailing comma
  "val": 0123,         // ❌ Leading zero
  // comment           // ❌ Comment
  "nan": NaN           // ❌ NaN is not JSON
}