sui-json.md

title
SuiJSON

Introduction

SuiJSON is a JSON-based format with restrictions that allow Sui to align JSON inputs more closely with Move Call arguments.

This table shows the restrictions placed on JSON types to make them SuiJSON compatible:

JSON	SuiJSON Restrictions	Move Type Mapping
Number	Must be unsigned integer	U8 U64 (U128 is encoded as String)
String	No restrictions	Vector<U8> Address ObjectID TypeTag Identifier Unsigned Integer (128 bit max)
Boolean	No restrictions	Bool
Array	Must be homogeneous JSON and of SuiJSON type	Vector
Null	Not allowed
Object	Not allowed

Type coercion reasoning

Due to the loosely typed nature of JSON/SuiJSON and the strongly typed nature of Move types, we sometimes need to overload SuiJSON types to represent multiple Move types.
For example SuiJSON::Number can represent both U8 and U64. This means we have to coerce and sometimes convert types.

Which type we coerce depends on the expected Move type. For example, if the Move function expects a U8, we must have received a SuiJSON::Number with a value less than 256. More importantly, we have no way to easily express Move addresses in JSON, so we encode them as hex strings prefixed by 0x.

Additionally, Move supports U128 but JSON doesn't. As a result we allow encoding numbers as strings.

Type coercion rules

Move Type	SuiJSON Representations	Valid Examples	Invalid Examples
Bool	Bool	true, false
U8	Three formats are supported Unsigned number < 256. Decimal string with value < 256. One byte hex string prefixed with 0x.	7 "70" "0x43"	-5: negative not allowed 3.9: float now allowed NaN: not allowed 300: U8 must be less than 256 " 9": Spaces not allowed in string "9A": Hex num must be prefixed with 0x "0x09CD": Too large for U8
U64	Similarly to U8, three formats are supported Unsigned number < U64::MAX. Decimal string with value < U64::MAX. Up to 8 byte hex string prefixed with 0x.	Extrapolate above examples	Extrapolate above examples
U128	Two formats are supported Decimal string with value < U128::MAX. Up to 16 byte hex string prefixed with 0x.	"74794734937420002470" "0x2B1A39A1514E1D8A7CE"	34: Although this is a valid u128 number, it must be encoded as a string
Address	20 byte hex string prefixed with 0x	"0x2B1A39A1514E1D8A7CE45919CFEB4FEE70B4E011"	0x2B1A39: string too short 2B1A39A1514E1D8A7CE45919CFEB4FEE70B4E011: missing 0x prefix 0xG2B1A39A1514E1D8A7CE45919CFEB4FEE70B4E01: invalid hex char G
ObjectID	16 byte hex string prefixed with 0x	"0x2B1A39A1514E1D8A7CE45919CFEB4FEE"	Similar to above
Identifier	Typically used for module and function names. Encoded as one of the following: A String whose first character is a letter and the remaining characters are letters, digits or underscore. A String whose first character is an underscore, and there is at least one further letter, digit or underscore	"function", "_function", "some_name", "____some_name", "Another"	"_": missing trailing underscore, digit or letter, "8name": cannot start with digit, ".function": cannot start with period, " ": cannot be empty space, "func name": cannot have spaces
Vector<Move Type>	Homogeneous vector of aforementioned types including nested vectors	[1,2,3,4]: simple U8 vector [[3,600],[],[0,7,4]]: nested U64 vector	[1,2,3,false]: not homogeneous JSON [1,2,null,4]: invalid elements [1,2,"7"]: although we allow encoding numbers as strings meaning this array can evaluate to [1,2,7], the array is still ambiguous so it fails the homogeneity check.
Vector<U8>	For convenience, we allow: U8 vectors represented as UTF-8 (and ASCII) strings.	"√®ˆbo72 √∂†∆˚–œ∑π2ie": UTF-8 "abcdE738-2 _=?": ASCII