ARC-20

ARC-20 is the Atomicals fungible token model on Bitcoin. One unit is one coloured satoshi. Everything else follows from that.

One unit is one satoshi. An ARC-20 balance is not a number stored somewhere. It is the satoshi value of the outputs a validator recognises as coloured for that token. An output worth 700 satoshis that a validator colours for a ticker carries exactly 700 units. Spending it spends the units. Splitting it splits the units, subject to the allocation rules.

One unit is one satoshi

An ARC-20 balance is not a number stored somewhere. It is the satoshi value of the outputs a validator recognises as coloured for that token. An output worth 700 satoshis that a validator colours for a ticker carries exactly 700 units. Spending it spends the units. Splitting it splits the units, subject to the allocation rules.

The complete model in seven statements

1. A unit is a satoshi in an output a validator recognises as coloured for a token.
2. Supply is therefore measured in satoshis, and is bounded by real bitcoin.
3. Issuance happens once, directly, or repeatedly through a deployment others mint against.
4. A ticker is a globally allocated name resolved to exactly one Atomical.
5. A transfer is an allocation over the transaction’s inputs and outputs, in order.
6. Value that cannot be placed in an eligible output is destroyed.
7. Coloured output totals can never exceed coloured input totals.

Statement six is the one people learn the expensive way

Read burns before you build or sign anything.

Where each rule is documented

Area	Page
The unit model and why decimals do not create fractions	Unit model
Ticker allocation, candidates, and verified winners	Tickers and candidates
One step issuance of a complete supply	Direct issuance
Deployments with a fixed number of mints	Fixed DFT
Claiming a mint against a deployment	Decentralised mint
Activation gated progressive deployments	Perpetual DFT
Work requirements on commit and reveal	Bitwork requirements
Optional metadata and presentation decimals	Metadata and decimals
How value is placed into outputs	Allocation
Separating and recombining coloured lots	Split and combine
How value is destroyed	Burns
Moving tokens and swapping them atomically	Transfers and swaps
What a PSBT must contain	PSBT requirements
What a wallet must do to be safe	Wallet safety
The status of Substantiation Factor material	Substantiation Factor

What ARC-20 is not

• Not an ERC-20 contract. There is no contract and no account.
• Not an inscription balance. Value is the satoshi value of outputs, not a number written in text.
• Not a claim on anything. Nothing backs a unit unless a separate legal arrangement exists, and none is created by minting.
• Not an ARC-721 standard. No official source located during review establishes one.

Universe product boundary

The protocol supports direct mint-ft issuance. No Universe product surface exposes it today. Universe exposes verified ticker resolution, token details, holders, confirmed activity, portfolio balances, coloured UTXOs, and Marketplace v1 flows. See status and known limitations.

• Allocation visualizer

  Model a transaction and see exactly where every unit lands.

• Conformance vectors

  The deterministic cases behind every number on these pages.