starchild-ai-agent/@1365/across-bridge

Across Bridge

Ultra-fast cross-chain token bridging with ~2 minute settlement times.

Prerequisites — Wallet Policy

Before executing any bridge, the wallet policy must be active. Load the wallet-policy skill and propose the standard wildcard policy (deny key export + allow *). This covers all across-bridge operations across all chains.

When to Use

Speed-critical cross-chain transfers:

• Speed first: 1-3 minutes vs 7+ days for native bridges
• Major routes: Arbitrum ↔ Base, ETH ↔ L2s, full mesh support
• Auto-conversion: USDT → USDC in single bridge operation
• Fee range: 0.05-0.5% (excellent for urgent transfers)

Core Decision Pattern

User request: "Bridge X tokens from Chain A to Chain B"

1. Single quote call → /swap API returns everything: quote, fees, transactions
2. Present quote → Expected output, fees (%), settlement time (~2 min)
3. Execute if approved → Send approvals (if needed) → Send bridge transaction
4. Verify completion → Check destination balance after ~2 minutes

Key insight: The /swap endpoint provides complete transaction data, not just quotes. One API call gives you everything needed to execute.

Quote Interpretation

Good bridge quotes:

• Fee <0.5% (competitive)
• Settlement <3 minutes (fast route)
• Output amount close to input (minimal conversion slippage)

Red flags:

• Fee >1% (expensive route, warn user)
• Settlement >10 minutes (congested route)
• Large output difference (poor liquidity)

Supported Assets & Chains

Chains: Ethereum, Arbitrum, Base, Optimism, Polygon
Tokens: ETH, WETH, USDC, USDT, DAI (most liquid pairs)

Popular routes:

• Arbitrum USDT → Base USDC (DeFi optimal)
• Ethereum ETH → Arbitrum ETH (L1 → L2)
• Base USDC → Arbitrum USDC (L2 ↔ L2)

Technical Implementation

Use the script for complex API interactions:

# Load the API helper
exec(open('skills/across-bridge/scripts/across_api.py').read())

# Get quote + transaction data
result = get_across_quote(
    input_token="0xFd086bC7CD5C481DCC9C85ebE478A1C0b69FCbb9",  # USDT on Arbitrum
    output_token="0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",  # USDC on Base
    amount="5000000",  # 5 USDT (6 decimals)
    origin_chain=42161,  # Arbitrum
    dest_chain=8453,  # Base
    depositor="0x..."  # User wallet
)

Response handling:

• result['expectedOutputAmount'] → tokens user will receive
• result['fees']['total'] → fee breakdown with percentage
• result['swapTx'] → ready-to-send bridge transaction
• result['approvalTxns'] → approval transactions (if needed)
• result['expectedFillTime'] → settlement minutes

Error Patterns

API failures:

• Missing depositor: Include wallet address in all calls
• Invalid amount format: Use string wei amounts ("5000000"), not numbers
• Unsupported route: Not all token pairs supported on all chains

Execution failures:

• Insufficient balance: Check balance before quoting
• Missing approvals: Send approvalTxns[] before bridge transaction
• High slippage: Routes with >1% fees may have poor liquidity

Always extract fee percentage and settlement time from quotes. Show both to user before executing.