Why a Second Edition?
ECMA-404 First Edition was published in October 2013. By 2017, the parallel IETF track had produced RFC 7159 and then RFC 8259, each with slightly different wording from the original Ecma document. Although the data model was the same, subtle differences in phrasing created uncertainty about which document to cite as authoritative and whether conformance to one implied conformance to the other.
The second edition, published in December 2017 simultaneously with RFC 8259, was produced to eliminate this confusion. The Ecma TC39 committee and the IETF JSON working group coordinated the text of both documents so that they describe the same thing in consistent language.
Alignment with RFC 8259
The second edition incorporates the clarifications made in RFC 8259. Most importantly, it aligns on the definition of a JSON text as a serialised value (removing the implicit restriction to objects and arrays at the top level that was present in RFC 4627) and adopts consistent grammar notation.
The two documents are intentionally complementary rather than redundant. ECMA-404 focuses exclusively on grammar; RFC 8259 adds IETF context such as the application/json MIME type, encoding requirements, and guidance for use in internet protocols. An application implementing both is in complete conformance with the JSON standard.
The Minimal Philosophy of ECMA-404
ECMA-404 is notably brief — fewer than ten pages. This is intentional. The document defines what constitutes a valid JSON text (the grammar) and what the data types are (objects, arrays, strings, numbers, booleans, null), but it deliberately says nothing about semantics: what values mean, how they should be interpreted, or what operations are valid on them.
This minimalism was a deliberate design choice by Douglas Crockford, who participated in the original ECMA-404 process. By keeping the specification free of semantic constraints, ECMA-404 is usable as a stable reference across an enormous range of applications without becoming obsolete as use cases evolve.
Which to Reference?
Both documents are authoritative. The practical guidance is:
- Cite ECMA-404 when you need a stable international standard reference for "what is JSON" in a context where the IETF track is not relevant — a programming language specification, a hardware interface, a data archive format.
- Cite RFC 8259 when you are working in an internet protocol context — an API specification, an HTTP content type definition, or an IETF draft. RFC 8259 is an IETF Internet Standard (not just an Informational RFC), which carries normative weight in IETF documents.
Citing both is common in standards documents that need to cover all bases.