Ion is a data serialization language developed by Amazon. It may be represented by either a human-readable text form or a compact binary form. The text form is a superset of JSON; thus, any valid JSON document is also a valid Ion document.

As a superset of JSON, Ion includes the following data types

• null: An empty value (for JSON compatibility)
• bool: Boolean values
• string: Unicode text literals
• list: Ordered heterogeneous collection of Ion values (extension of JSON array)
• struct: Unordered collection of key/value pairs (extension of JSON object)

The nebulous JSON 'number' type is strictly defined in Ion to be one of

• int: Signed integers of arbitrary size
• float: 64-bit IEEE binary-encoded floating point numbers
• decimal: Decimal-encoded real numbers of arbitrary precision

Ion adds these types:

• timestamp: Date/time/time zone moments of arbitrary precision
• symbol: Unicode symbolic atoms (aka identifiers), stored as interned strings in binary format
• blob: Binary data of user-defined encoding
• clob: Text data of user-defined encoding
• sexp: Nested list of values (equivalent to an S-expression) with application-defined semantics

Each Ion type supports a null variant, indicating a lack of value while maintaining a strict type (e.g., null.int, null.struct).

The Ion format permits attaching one or more annotations (i.e. a list of symbols) to any value. Such annotations may be used as metadata for otherwise opaque data (such as a blob).

• Amazon supported library implementations
• C#
• Go Lang
• Python
• JS

Features seen in JavaScript and JSON5:

// Comments are allowed using the double forward slash 
{
key:"value",// key here is a symbol, it can also be a string as in JSON
nums:1_000_000,// equivalent to 1000000, use of underscores with numbers is more readable
"A float":31415e-4,// key is a value that contains spaces 
}

Features unique to Ion:

{
symbol:'a symbol',// symbols are interned Unicode strings
"A null integer":null.int,
annotated:age::35,// the symbol "age" is attached to the value "35" as an annotation
lists:'hw grades'::[80,85,90],// any symbol can be used as an annotation 
many_annot:I::have::many::annotations::true,// annotations are not nested, but rather, a list of annotations
sexp:(this(isa[valid]"Ion")last::value+42)// Ion S-expressions. 'this', 'is', 'a', 'valid', 'value', and '+' are symbols.
_value:{{OiBTIKUgTyAASb8=}},// blob value is represented as base64
_value:{{"a b\0\xff"}}// clob value is represented as an ASCII string with C-style escapes
// ^ repeated names (keys) are allowed but generate a warning for undefined behavior 
}

• Amazon's Quantum Ledger Database (QLDB) stores data in Ion documents.^[1]
• PartiQL, an open source SQL-based query language also by Amazon, is built upon Ion. PartiQL supported queries are used by QLDB, S3Select.^[2]

• Ion Path Extractor API aims to combine the convenience of a DOM API with the speed of a streaming API.
• IDE support
  • Eclipse
  • IntelliJ
• Jackson data format module for Ion
• Apache Hive SerDe for Ion
• Ion Schema
  • Specification
  • Implementations
• Ion Hash defines an algorithm for constructing a hash for any Ion value, given a user-provided hash function capable of taking binary data of arbitrary length.
  • Specification
  • Implementations

• Ion specification
• Amazon supported language implementations
• Java API documentation
• C# implementation