across-bridge

name	across-bridge
version	1.0.0
description	Bridge ETH and ERC-20 tokens across EVM chains via Across Protocol v3. One function for a quote, one function for the entire end-to-end bridge (approval + deposit + arrival verification). Use when the user wants to move tokens between chains (e.g. "bridge 50 USDC from Base to Arbitrum", "send ETH from Ethereum to Optimism", "move USDT Arbitrum → Base"). Supports Ethereum, Arbitrum, Optimism, Base, Polygon, BSC, Linea, zkSync, Scroll, Mantle. Fast settlement (seconds to minutes).
author	starchild
tags	["bridge","defi","cross-chain","across","evm","ethereum","arbitrum","base","optimism"]
delivery	script
metadata	{"starchild":{"emoji":"🌉","skillKey":"across-bridge","requires":{"bins":["python3"]},"install":[{"kind":"pip","package":"requests"}]}}

🌉 Across Bridge

Bridge tokens between EVM chains using Across Protocol v3. Across is an intent-based bridge: relayers front the liquidity on the destination chain and get repaid on the origin chain, so settlement is fast (seconds to a few minutes) and fees are low (0.05–0.5%).

When to Use

• Cross-chain token transfer: "bridge 50 USDC from Base to Arbitrum"
• L1 ↔ L2 movement: "send 0.01 ETH from Ethereum to Optimism"
• Stablecoin hops: "move USDT from Arbitrum to Base"
• Speed matters: Across fills in seconds–minutes vs native bridges (7 days)

Supported Chains

Ethereum · Arbitrum · Optimism · Base · Polygon · BSC · Linea · zkSync · Scroll · Mantle

Supported Tokens

ETH · WETH · USDC · USDT · WBTC · DAI

How to Call

All operations are Python functions exposed under core.skill_tools. Because the skill name contains a hyphen, use the _modules dict to access it:

python3 - <<'EOF'
from core.skill_tools import _modules
across = _modules["across-bridge"]
import json
q = across.bridge_quote(from_chain="base", to_chain="arbitrum",
                        token="USDC", amount=1, wallet="0x...")
print(json.dumps(q, indent=2))
EOF

bridge_quote(from_chain, to_chain, token, amount, wallet=None)

Get a live quote — no on-chain action. Returns output amount, fees, estimated fill time, and (if wallet is provided) ready-to-sign approval + bridge transactions.

bridge_execute(from_chain, to_chain, token, amount, wallet, confirm_arrival=True)

One call does everything:

1. Fetches a fresh quote from Across /swap
2. Sends ERC-20 approval to the SpokePool (if needed; skipped for native ETH)
3. Sends the depositV3 bridge transaction
4. Polls the destination-chain balance until funds arrive (or timeout)

Returns a full receipt with status, output_amount, approval_tx, bridge_tx, and arrival_confirmed.

bridge_status(origin_chain, deposit_tx_hash)

Check the fill status of a submitted deposit via Across's status API.

Workflows

Just get a quote (no execution)

python3 - <<'EOF'
from core.skill_tools import _modules
across = _modules["across-bridge"]
import json
q = across.bridge_quote(from_chain="base", to_chain="arbitrum",
                        token="USDC", amount=50)
print(json.dumps(q, indent=2))
EOF

Key fields in the response:

• output_amount_human — tokens the recipient will receive
• fees.total_pct — fee percentage (e.g. 4688000000000000 = 0.47%)
• estimated_fill_time_sec — expected settlement time
• needs_approval — whether an ERC-20 approve is required before bridging

Bridge end-to-end (the common case)

python3 - <<'EOF'
from core.skill_tools import _modules
across = _modules["across-bridge"]
import json
r = across.bridge_execute(from_chain="base", to_chain="arbitrum",
                          token="USDC", amount=1,
                          wallet="0x0B52...Eb16")
print(json.dumps(r, indent=2, default=str))
EOF

That single call handles approval + deposit + arrival verification. No need to manually call wallet_transfer or encode calldata — the Across /swap API returns ready-to-sign transactions and this skill dispatches them.

Check status of a submitted deposit

python3 - <<'EOF'
from core.skill_tools import _modules
across = _modules["across-bridge"]
import json
s = across.bridge_status(origin_chain="base", deposit_tx_hash="0x...")
print(json.dumps(s, indent=2))
EOF

Acceptance / Red-Flag Guidance

Good routes:

• Fee < 0.5% · fill time < 60s · output ≈ input (minus small fee)

Warn the user before proceeding if:

• Fee > 1% (expensive route or very small amount — min deposit applies)
• Fill time > 10 minutes (congested route)
• Amount below limits.min_deposit (quote will flag isAmountTooLow)

Key Facts

• Native ETH: msg.value carries the amount; no approval step. Across handles wrapping/unwrapping automatically.
• ERC-20: msg.value = 0; an approve(spokePool, amount) is required first. bridge_execute sends this automatically.
• Quotes are live from app.across.to/api/swap and valid for ~30s. bridge_execute re-fetches right before broadcasting.
• Gas is sponsored by default via the Starchild wallet — the user doesn't need native tokens on the origin chain for gas.
• Settlement: Across relayers typically fill within seconds to a few minutes. bridge_execute polls the destination balance for up to 180s.
• Wallet: uses the Starchild Agent Wallet (same as the wallet skill). No separate wallet connection needed.

Dependencies

• requests (pip)
• core.skill_tools.wallet (platform — for signing/broadcasting)

Tested Routes

This skill was validated with a real on-chain bridge: 1 USDC Base → Arbitrum, confirmed arrived on destination within ~35 seconds, fee 0.47%.