@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