Token Metadata Standards

Mintlayer tokens carry their identity off-chain: an issuance transaction stores a metadata URI, and the JSON document served at that URI describes the token to wallets, explorers, and marketplaces. The token-standards repository defines the recommended schemas for those documents:

MLS-01: fungible tokens (mls01.md)
MLS-03: non-fungible tokens, NFTs (mls03.md)

The repository is the canonical reference: it contains the full schema descriptions plus ready-made example files for every token type (e.g. mls01/utility.json, mls03/art.json).

Off-chain by design

Metadata is not validated by consensus. The chain enforces what is on-chain (ticker, decimals, supply, authority, the metadata URI itself); the JSON standard below exists so that issuers publish consistent, machine-readable metadata that every client can render the same way.

Where the URI is set

Token kind	Set at issuance	Changeable
MLS-01 fungible	`metadata_uri` field of the issuance transaction	Yes, via the token authority; see Update the metadata URI
MLS-03 NFT	`metadata_uri` / additional metadata URI at issuance	No: NFT metadata is immutable once issued

Common top-level fields

All token metadata (both MLS-01 and MLS-03) shares these base fields:

Field	Type	Description
`schema_version`	string	Schema version, e.g. `"1.0"`
`token_type`	string	Discriminator, drives the shape of `type_metadata`
`name`	string	Human-readable token name
`symbol`	string	Ticker symbol
`description`	string	Short description
`logo_uri`	string	Image URI for the token logo
`website`	string	Official website
`social`	object	Social/community links (twitter, discord, telegram, github, whitepaper)
`type_metadata`	object	Type-specific fields, shape varies by `token_type`
`cross_chain`	array	Bridge/cross-chain contract addresses
`market`	object	Exchange listings, launch price, data feed IDs
`certifications`	array	Third-party certifications

Shared blocks

`cross_chain`

Lists representations of the token on other chains, with the bridge that produced them:

"cross_chain": [
  {
    "chain": "ethereum",
    "chain_id": 1,
    "address": "0x...",
    "standard": "ERC20",
    "bridge_protocol": "Mintlayer Bridge",
    "bridge_type": "canonical",
    "verified": true
  }
]

bridge_type values: canonical (official deployment controlled by the token team), bridged (third-party bridge, not controlled by the issuer), wrapped (wrapped version with a different custodian).

`market`

Exchange listings, launch data, and aggregator IDs:

"market": {
  "launch_date": "2024-01-15",
  "launch_price_usd": 0.05,
  "exchanges": [
    { "name": "Binance", "type": "cex", "pairs": ["MTK/USDT"], "url": "https://...", "listed_date": "2024-02-01" },
    { "name": "Uniswap V3", "type": "dex", "chain": "ethereum", "pairs": ["MTK/USDC"] }
  ],
  "coingecko_id": "mytoken",
  "coinmarketcap_id": "12345"
}

`certifications`

A general array for any third-party certification; the type field drives optional detail blocks (e.g. shariah_details). Supported types include shariah, esg, halal, carbon_neutral, and other:

"certifications": [
  {
    "type": "shariah",
    "label": "Shariah Compliant",
    "standard": "AAOIFI",
    "certifying_body": { "name": "Amanie Advisors", "jurisdiction": "MY", "website": "https://..." },
    "reference": "FATWA-2024-007",
    "issued_date": "2024-03-01",
    "expiry_date": "2025-03-01",
    "status": "active",
    "document_url": "https://...",
    "document_hash": "sha256:..."
  }
]

Example

A minimal MLS-01 utility token (mls01/utility.json):

{
  "schema_version": "1.0",
  "token_type": "utility",
  "name": "Example Utility Token",
  "symbol": "EXT",
  "decimals": 8,
  "description": "A general-purpose utility token used for network fees and access to protocol services.",
  "logo_uri": "https://example.com/logo.png",
  "website": "https://example.com",
  "social": { "twitter": "https://twitter.com/exampletoken" },
  "type_metadata": {},
  "cross_chain": [],
  "market": {},
  "certifications": []
}

Where the URI is set​

Common top-level fields​

Shared blocks​

cross_chain​

market​

certifications​

Example​