CTMeta Standard

Introduction

CKB Transaction Metadata (aka. CTMeta) is the standard of additional metadata for transactions, tokens, and smart contracts on Nervos CKB. It dramatically reduces CKB state cost by using witness as the static data storage space. The typical user scenarios of CTMeta include transaction postscript, token definition, NFT description, and so on.

The convention

CTMeta uses group_witnesses[0].output_type as the data container. The data should be written in Json format, with the following schema.

{
    "id": "CTMeta",              // identifier for off-chain processor
    "ver": "1.0",                // current version
    "metadata":                  
    [
        {
            "target": "output#0",    // description for which utxo, format: {input, output}#index
            "type": "nft-renderer",  // metadata types
            "data": <payload_data>   // detail metadata for various types
        },
        {
            "target": "output#1",    // an example for transfer postscript
            "type": "postscript",
            "data": "I love you."
        },
        // ...
    ]
}

Pre-defined metadata type

schema type	description	schema standard
cota.nft.define*	CoTA NFT definition	CoTA NFT Metadata Schema
cota.ft.define	CoTA FT definition	CoTA Fungible Token Metadata Schema
issuer	cota token issuer information	WIP
postscript	general transfer postscript for ckb/sudt/nft	UTF-8 encoded
sudt-info	sudt definition	WIP

* In previous design, the CoTA NFT definition schema type is cota. To keep compatibility, cota.nft.define and cota will both valid.