Overview
RGB is a system of smart contracts that operates on top of Bitcoin and the Lightning Network. Unlike blockchain-based smart contract platforms that store all contract data on-chain, RGB keeps contract state and logic entirely off-chain, using Bitcoin transactions only as "anchors" to commit to state transitions. This client-side validation approach avoids blockchain bloat while leveraging Bitcoin's security.
How RGB Works
RGB Architecture:
┌─────────────────────────────────────────────┐
│ Off-Chain (Client-Side) │
│ │
│ ┌──────────┐ ┌──────────┐ ┌─────────┐ │
│ │ Contract │ │ State │ │ State │ │
│ │ Schema │──>│ Trans. 1 │──>│ Trans.2 │ │
│ │ (rules) │ │ │ │ │ │
│ └──────────┘ └────┬─────┘ └────┬────┘ │
│ │ │ │
└──────────────────────┼──────────────┼───────┘
│ │
┌──────────▼──────────────▼──────┐
│ Bitcoin Blockchain │
│ │
│ TX1 (commitment) TX2 (commit) │
│ Only a hash of Only a hash │
│ the state change of the state │
│ is anchored change │
└────────────────────────────────┘
Key insight: Bitcoin transactions carry tiny commitments
to off-chain state transitions
Client-Side Validation
The defining feature of RGB is client-side validation. Instead of every node validating every contract (as in Ethereum), only the parties involved in a transaction validate the relevant contract state. When receiving an RGB asset, the recipient validates the entire history of state transitions for that specific asset, ensuring correctness without relying on global consensus.
Capabilities
- Token issuance — Create fungible tokens (similar to ERC-20) anchored to Bitcoin
- NFTs and collectibles — Issue unique digital assets with provable scarcity
- Complex contracts — Define rules for asset transfers, vesting schedules, and other programmable conditions
- Lightning compatibility — RGB assets can be transferred over Lightning payment channels, enabling instant and private asset transfers
Privacy Benefits
Because contract data is stored off-chain and shared only between participants, RGB provides strong privacy. Blockchain observers cannot determine what assets are being transferred or even that an RGB transaction is occurring — they see only ordinary Bitcoin transactions.
Trade-offs
- Data availability — Recipients must be able to obtain the full state transition history for validation. If this data is lost, the asset becomes unspendable.
- Complexity — Client-side validation and off-chain state management add implementation complexity compared to on-chain smart contracts.
- Ecosystem maturity — RGB is still relatively young compared to established on-chain smart contract platforms.
Common Misconception
RGB does not create a separate blockchain or sidechain. It uses Bitcoin transactions directly as commitment anchors. The "smart contract" layer exists entirely as data exchanged between parties and validated locally, making it fundamentally different from platforms like Ethereum or even Bitcoin sidechains.