starchild-ai-agent/@1247/across-bridge

Across Protocol Bridge Skill

Bridge ETH and ERC-20 tokens between EVM chains using Across Protocol v3 SpokePool.

Supported Chains

| Chain | Chain ID | |-------|----------| | Ethereum | 1 | | Arbitrum | 42161 | | Optimism | 10 | | Base | 8453 | | Polygon | 137 | | BSC | 56 | | Linea | 59144 | | zkSync Era | 324 |

Supported Tokens

| Token | Notes | |-------|-------| | ETH | Native ETH (bridged via WETH internally) | | USDC | Native USDC where available | | USDT | Major chains | | WBTC | Ethereum, Arbitrum, Optimism | | DAI | Major chains |

Workflow

1. Get a Quote + Build Transaction

pip install requests eth-abi
python3 skills/across-bridge/scripts/bridge.py <from_chain_id> <to_chain_id> <amount_wei> <wallet_address> [token_symbol]

Examples:

Bridge 0.01415 ETH from Arbitrum to Ethereum:

python3 skills/across-bridge/scripts/bridge.py 42161 1 14150000000000000 0xYourWallet

Bridge 100 USDC from Base to Arbitrum:

python3 skills/across-bridge/scripts/bridge.py 8453 42161 100000000 0xYourWallet USDC

The script outputs a JSON object with:

• to — SpokePool contract address on origin chain
• value — ETH value to send (amount for ETH bridges, "0" for ERC-20)
• data — encoded depositV3() calldata
• output_amount_wei — amount you'll receive on destination
• estimated_fill_time_sec — estimated seconds to receive funds
• note — for ERC-20: reminder to approve the SpokePool before sending

2. ERC-20 Approval (skip for ETH)

For ERC-20 tokens (USDC, USDT, etc.), approve the SpokePool to spend your tokens first:

# Approve call: token.approve(spokePool, amount)
# Use wallet_transfer with the token contract's approve() calldata

The script output includes a note field with the token address and SpokePool address when approval is needed.

3. Execute the Transaction

wallet_transfer(
    to="<SpokePool address from script>",
    amount="<value from script>",   # amount_wei for ETH, "0" for ERC-20
    chain_id=<origin chain id>,
    data="<data from script>"
)

4. Track Deposit Status

After broadcasting, check fill status using the deposit tx hash:

python3 skills/across-bridge/scripts/bridge.py status <origin_chain_id> <deposit_tx_hash>

Or verify arrival directly:

wallet_balance(chain=<destination_chain>)

Across relayers typically fill within seconds to a few minutes. The estimated_fill_time_sec from the quote gives a per-route estimate.

Usage Example

User: "Bridge 50 USDC from Base to Arbitrum"

1. Run the script with token=USDC, from=8453, to=42161, amount=50000000
2. Check the note field — approve USDC to SpokePool if needed
3. Call wallet_transfer with the encoded calldata
4. After tx confirms, run status check or call wallet_balance(chain="arbitrum") to confirm arrival

Notes

• ETH bridges: msg.value = amount (no approval needed)
• ERC-20 bridges: msg.value = 0, token approval required first
• Fees are deducted from output amount (~0.01–0.1% typically, varies by route)
• Quotes are live from app.across.to/api/suggested-fees — valid for ~30s
• exclusivityDeadline is handled correctly whether the API returns an offset or absolute timestamp

Dependencies

requests
eth-abi

Install: pip install requests eth-abi