| name | cross-chain-bridge |
| description | Build cross-chain messaging and asset bridging — lock-and-mint, liquidity networks, and message verification |
| allowed-tools | ["Read","Write","Grep"] |
| effort | high |
When to activate
- Building token bridges between EVM chains
- Implementing cross-chain messaging protocols
- Designing wrapped asset mechanisms (wrapped ETH on Polygon, etc.)
- Integrating existing bridges (LayerZero, Wormhole, Axelar)
- Building cross-chain NFT bridges
When NOT to use
- For single-chain applications
- For centralized exchange transfers
- For off-chain cross-database synchronization
Instructions
- Choose bridge pattern. Lock-and-mint (canonical), liquidity network (fast), or message-passing (general).
- Select verification. Validators (centralized), optimistic (fraud proofs), or light client (trustless but expensive).
- Implement lock side. Deposit contract, event emission, nonce tracking, replay protection.
- Implement mint side. Verification of source chain event, mint/claim function, replay protection.
- Handle edge cases. Source chain reorgs, validator downtime, stuck transactions, partial fills.
- Security. Multi-sig for validators, rate limiting, maximum bridge amounts, emergency pause.
- Testing. Simulate both chains with Foundry. Test reorg scenarios, validator failures, concurrent bridges.
Example
Lock-and-Mint Bridge Flow:
Source Chain (Ethereum):
1. User deposits 1 ETH to Bridge contract
2. Bridge emits LockedEvent(user, amount, destinationChain, nonce)
3. Relayer picks up event
Destination Chain (Polygon):
4. Relayer submits proof of LockedEvent
5. Verifier confirms event authenticity (validator signatures)
6. Bridge mints 1 WETH on Polygon to user
7. User can redeem WETH back to ETH via reverse flow
