Swap CLI

Use fynd-swap-cli to dry-run and execute swaps against a running Fynd server.

fynd-swap-cli is a CLI binary for quoting, simulating, and executing swaps. It's useful for quick testing from the terminal without writing any code.

Prerequisites

1. Running Fynd server — start fynd serve first. See the Quickstart if you haven't.

2. RPC URL — required for simulation and on-chain execution. The default public endpoint (https://eth.llamarpc.com) does not support state overrides, so you must supply your own.

Build

cargo build --release -p fynd-swap-cli
# binary: target/release/fynd-swap-cli

Dry-run a swap (ERC-20)

By default, fynd-swap-cli runs a dry-run: it generates an ephemeral key and injects ERC-20 storage overrides so the simulation succeeds without any real funds or wallet approvals.

export RPC_URL=https://your-rpc-provider.com/v1/your_key

./target/release/fynd-swap-cli \
  --sell-token  0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48 \
  --buy-token   0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2 \
  --sell-amount 1000000000

The output prints the quote (amount_in, amount_out, gas estimate, route) followed by the simulation result.

--sell-amount is in raw atomic units. 1 000 000 000 = 1000 USDC (6 decimals). 1 000 000 000 000 000 000 = 1 WETH (18 decimals).

Dry-run a swap (Permit2)

Add --transfer-type transfer-from-permit2 and supply the TychoRouter address with --router. The dry-run uses nonce 0 and maximum deadlines, so you don't need any chain reads for Permit2 state.

export RPC_URL=https://your-rpc-provider.com/v1/your_key

./target/release/fynd-swap-cli \
  --sell-token    0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48 \
  --buy-token     0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2 \
  --sell-amount   1000000000 \
  --transfer-type transfer-from-permit2 \
  --router        <TychoRouter address>

Find the TychoRouter address for your chain in the Tycho contract addresses.

Execute on-chain (ERC-20)

Add --execute and set PRIVATE_KEY. The CLI will verify that the router has sufficient allowance before submitting and will print the required cast send approval command if it doesn't.

This sends a real transaction. Ensure your wallet has the sell token and has approved the TychoRouter to spend it before running with --execute.

export RPC_URL=https://your-rpc-provider.com/v1/your_key
export PRIVATE_KEY=your_private_key_hex   # no 0x prefix

./target/release/fynd-swap-cli \
  --sell-token  0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48 \
  --buy-token   0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2 \
  --sell-amount 1000000000 \
  --execute

Execute on-chain (Permit2)

Add --execute --transfer-type transfer-from-permit2 --router <addr>. The CLI reads the current Permit2 nonce from the contract, builds the EIP-712 permit, signs it with your key, and submits the swap in one step.

Your wallet must have already approved the Permit2 contract (0x000000000022D473030F116dDEE9F6B43aC78BA3) to spend the sell token. The CLI prints the required cast send command if that approval is missing.

export RPC_URL=https://your-rpc-provider.com/v1/your_key
export PRIVATE_KEY=your_private_key_hex   # no 0x prefix

./target/release/fynd-swap-cli \
  --sell-token    0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48 \
  --buy-token     0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2 \
  --sell-amount   1000000000 \
  --transfer-type transfer-from-permit2 \
  --router        <TychoRouter address> \
  --execute

Swap using vault funds

If tokens are already deposited in the Tycho Router vault, use --transfer-type use-vaults-funds. No ERC-20 approval or Permit2 signature is needed.

./target/release/fynd-swap-cli \
  --sell-token 0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48 \
  --buy-token 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2 \
  --sell-amount 1000000000 \
  --transfer-type use-vaults-funds

---

Embedded server (no separate fynd serve needed)

If you don't want to run fynd serve separately, pass --tycho-url and fynd-swap-cli will spawn its own embedded solver automatically.

export TYCHO_API_KEY=your_api_key
export RPC_URL=https://your-rpc-provider.com/v1/your_key

./target/release/fynd-swap-cli \
  --tycho-url tycho-fynd-ethereum.propellerheads.xyz \
  --sell-amount 1000000000

This is convenient for a one-off swap but slow to initialize on every run (the solver must sync protocol state from Tycho before it can serve quotes). For repeated use, keep fynd serve running and omit --tycho-url.

CLI Reference

Flag	Env var	Default	Description
--sell-token	—	USDC (mainnet)	Token address to sell
--buy-token	—	WETH (mainnet)	Token address to buy
--sell-amount	—	1000000000	Amount to sell in raw atomic units
--slippage-bps	—	50 (0.5%)	Slippage tolerance in basis points
--fynd-url	—	http://localhost:3000	Fynd server URL (ignored when --tycho-url is set)
--transfer-type	—	transfer-from	transfer-from, transfer-from-permit2, or use-vaults-funds
--execute	—	false (dry-run)	Submit the swap on-chain. Requires PRIVATE_KEY.
--router	—	—	TychoRouter address. Required for transfer-from-permit2.
--permit2	—	0x000000000022D473030F116dDEE9F6B43aC78BA3	Permit2 contract address
--rpc-url	RPC_URL	https://eth.llamarpc.com	Ethereum RPC endpoint
--chain	—	Ethereum	Target chain
--tycho-url	—	—	If set, spawns an embedded Fynd solver connecting to this Tycho WebSocket URL
--tycho-api-key	TYCHO_API_KEY	—	Tycho API key (required when --tycho-url is set)
--disable-tls	—	false	Disable TLS for the Tycho WebSocket connection
--protocols	—	(all on-chain, fetched from Tycho)	Comma-separated protocols to index. Only used with --tycho-url.
--worker-pools-config	—	—	Path to worker pools TOML config. Only used with --tycho-url.
--http-port	—	3000	HTTP port for the embedded solver. Only used with --tycho-url.

Security Notes

1. Never expose your private key. Use the PRIVATE_KEY environment variable, never a CLI argument. Run unset HISTFILE before setting it to prevent it from being saved to your shell history.

2. Dry-run first. The default mode (no --execute) simulates the full swap with storage overrides — no funds needed. Confirm the output looks correct before adding --execute.

3. Slippage protection. The default 0.5% slippage may not be sufficient for large trades or volatile markets. Adjust --slippage-bps accordingly.

4. Mainnet warning. --execute sends a real transaction. Start with small amounts. All routes execute through the Tycho Router contract.

5. Verify routes. The CLI prints the full route before executing. Multi-hop routes through low-liquidity pools can result in worse execution.

6. Prices are indicative. Quotes reflect the best route at query time but are not guaranteed on-chain. Pool states change every block, and the longer you wait to execute, the more the price may drift.

Troubleshooting

"Solver is not healthy": Wait for the solver to finish loading market data. Check the fynd serve terminal for progress, or poll curl http://localhost:3000/v1/health.

"Sell/buy token not found": Ensure the token address is correct and the token exists on Tycho's indexer.

"No route found": Fynd couldn't find a path between your tokens. Check that both tokens have enough on-chain liquidity.

"Insufficient allowance": The CLI prints the exact cast send approval command needed. Run it, then retry.