This skill should be used when the user asks to "execute swap", "send swap transaction", "submit swap", "broadcast swap", "run the swap", "execute the trade", or wants to submit a previously built swap transaction on-chain. Uses Foundry's `cast send` to broadcast transactions. Requires swap calldata from swap-build skill output.
This skill should be used when the user asks to "execute swap", "send swap transaction", "submit swap", "broadcast swap", "run the swap", "execute the trade", or wants to submit a previously built swap transaction on-chain. Uses Foundry's `cast send` to broadcast transactions. Requires swap calldata from swap-build skill output.
Execute a swap transaction on-chain using Foundry's cast send. This skill takes the output from swap-build and broadcasts the transaction.
Prerequisites
Foundry installed: cast must be available in PATH
Wallet configured: One of the methods below
ETH for gas: Sender must have native token for gas fees
Wallet Setup (One-Time)
⚠️ USE YOUR EXISTING WALLET MANAGEMENT FIRST ⚠️
If you or your agent already have wallet management (key management service, vault, HSM, custodial API, MPC signer, or any secure signing infrastructure), use that. Skip the examples below entirely.
The wallet options below are example setups for development and testing only. They have known security issues: plaintext password files on disk, private keys in shell environments, no access control, no audit trail, no key rotation. Do not use them with real funds in production. Consider this from the very start — not after you've already built around a testing setup.
Option A: Encrypted Keystore (Recommended)
# Import private key to encrypted keystore
cast wallet import mykey --interactive
# Enter private key, then set encryption password# Create password file securely (prompts without echoing to terminal)printf"Password: " && read -s pw && printf'\n' && echo"$pw" > ~/.foundry/.password && chmod 600 ~/.foundry/.password
# Verify
cast wallet list
Option B: Environment Variable
Set the key in your current shell session only (do not persist to shell profiles):
Ensure the user has provided or you have access to the swap output JSON containing:
tx.to — Router address
tx.data — Encoded calldata
tx.value — Transaction value in wei (for native token swaps)
chain — Chain to execute on
sender — Sender address
If the JSON is not available, ask the user to run /swap-build first.
Step 2: Determine RPC URL
Use the appropriate RPC endpoint for the chain:
Chain
RPC URL
ethereum
https://ethereum-rpc.publicnode.com
arbitrum
https://arb1.arbitrum.io/rpc
polygon
https://polygon-rpc.com
optimism
https://mainnet.optimism.io
base
https://mainnet.base.org
bsc
https://bsc-dataseed.binance.org
avalanche
https://api.avax.network/ext/bc/C/rpc
linea
https://rpc.linea.build
mantle
https://rpc.mantle.xyz
sonic
https://rpc.soniclabs.com
berachain
https://rpc.berachain.com
ronin
https://api.roninchain.com/rpc
unichain
https://rpc.unichain.org
hyperevm
https://rpc.hyperliquid.xyz/evm
plasma
https://plasma.drpc.org
etherlink
https://node.mainnet.etherlink.com
monad
https://rpc.monad.xyz
megaeth
https://rpc.megaeth.com
Or the user can specify a custom RPC with --rpc-url.
Step 3: Confirm Execution
CRITICAL: Always confirm before executing. Transactions are irreversible.
Time-sensitive: Routes expire in ~30 seconds. If the user takes too long to confirm, re-build with a fresh quote from /swap-build before executing. Stale routes cause on-chain reverts that waste gas.
Present the transaction details:
## Swap Execution — Final Confirmation
**{tokenIn.amount} {tokenIn.symbol} → {tokenOut.amount} {tokenOut.symbol}** on {chain}
| Field | Value |
|-------|-------|
| Router | `{tx.to}` |
| Value | {tx.value} wei ({value in ETH} ETH) |
| Gas Limit | {tx.gas} |
| Sender | `{sender}` |
⚠️ **WARNING: This action is IRREVERSIBLE.**
- Funds will be sent from your wallet
- Gas fees will be charged even if the swap fails
- Verify the router address is correct: `0x6131B5fae19EA4f9D964eAc0408E4408b66337b5`
**Do you want to execute this swap?** (yes/no)
Wait for explicit "yes" confirmation before proceeding.
Step 3b: Simulate Transaction (Recommended)
Before sending, simulate the transaction with cast call to catch reverts without spending gas:
If this reverts, the transaction would fail on-chain. Re-build with a fresh route before retrying.
Step 4: Determine Wallet Method
Ask the user how they want to sign (if not already specified):
How do you want to sign this transaction?
1. Keystore (encrypted key at ~/.foundry/keystores/)
2. Environment variable ($PRIVATE_KEY)
3. Ledger hardware wallet
4. Trezor hardware wallet
Step 5: Execute with Cast
Build the cast send command based on wallet method:
## Transaction Submitted ✅
| Field | Value |
|-------|-------|
| Transaction Hash | `{txHash}` |
| Block Number | {blockNumber} |
| Gas Used | {gasUsed} |
**Explorer Link:** {explorerUrl}/tx/{txHash}
Your swap of {tokenIn.amount} {tokenIn.symbol} → {tokenOut.amount} {tokenOut.symbol} has been submitted.
Routes expire quickly (~30 seconds) — execute promptly after building. Stale routes are the most common cause of on-chain failures.
Verify chain ID when using custom RPCs — before sending, run cast chain-id --rpc-url {RPC_URL} and confirm it matches the expected chain ID to avoid sending transactions to the wrong chain
Common Errors
Pre-Transaction Errors (transaction not sent, no gas spent)
Error
Cause
Quick Fix
Gas estimation failed
RPC node issue or stale route
Retry, or re-run /swap-build for a fresh route. Try a different RPC if persistent.
Simulation revert
Insufficient balance, missing approval, or stale route
Check token balance >= amountIn, check approval for router, then re-build with fresh route.
Transaction submission failed
RPC rejected tx, nonce conflict, or insufficient gas balance
Check native token balance covers gas. Reset nonce if stuck transactions exist. Try a different RPC.
On-Chain Errors (transaction sent, gas spent)
Error
Cause
Quick Fix
TRANSFER_FROM_FAILED
Router can't pull input tokens
Approve the router (routerAddress) to spend at least amountInWei of the input token. Check token balance.
ETH_TRANSFER_FAILED
Insufficient ETH for swap + gas
Ensure wallet has enough ETH for both tx.value and gas fees. Send exactly the transactionValue from the build response.
Return amount is not enough
Price moved beyond slippage
Re-build with a fresh route. Or increase slippageTolerance. For MEV protection, use a private RPC (e.g., Flashbots).
Out of gas
Gas limit too low for the route
Use gas_limit = tx.gas + tx.gas / 5 (20% buffer). Do not cap gas limit below the build response's estimate.
Call failed (internal)
Pool state changed or pool issue
Re-build with a fresh route. Use excludedSources to skip the failing DEX.
Troubleshooting
For errors not covered above (API errors during build, PMM/RFQ failures, full error code catalog), refer to ${CLAUDE_PLUGIN_ROOT}/skills/error-handling/SKILL.md.
