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Gasless Swap

Swap tokens without paying gas fees. AchSwap's gasless mode lets you sign a transaction and have the relayer submit it on your behalf.

What Is Gasless Swap?​

Gasless swap is a meta-transaction system where:

  1. You sign a swap request off-chain
  2. The relayer submits the transaction and pays the gas
  3. Your tokens are transferred via Permit2 authorization

You never need to hold native USDC for gas — only the tokens you want to swap.

How It Works​

The Flow​

1. Enable Gasless Mode (Zap icon)
2. Approve Permit2 (one-time per token)
3. Enter swap details
4. Sign the permit message
5. Relayer submits transaction
6. Swap confirmed

Permit2 Authorization​

Gasless swaps use Permit2, a standard token authorization contract:

  • First use: Approve your token to Permit2, then approve Permit2 to the AchSwap Gasless contract
  • Subsequent uses: No approval needed (valid for 1 year)
  • Revocable: You can revoke approval at any time through your wallet

Signing Process​

When you click Swap in gasless mode:

  1. Your wallet shows a signature request
  2. This signs a SignedExecution message containing:
    • Swap parameters (tokens, amounts, slippage)
    • A unique nonce (prevents replay)
    • Deadline timestamp
  3. The signed message is sent to the relayer
  4. The relayer verifies and submits the transaction

Enabling Gasless Mode​

  1. Click the Zap icon in the swap header
  2. The icon turns green when active
  3. If Permit2 is not approved, click Enable Permit2 for Gasless
  4. Confirm the approval in your wallet (one-time per token)

Supported Operations​

OperationGasless Support
Token swap (V2)Yes
Token swap (V3 single-hop)Yes
Token swap (V3 multi-hop)Yes
Token swap (V4)Yes
Aggregator swap (split routing)Yes
Wrap/UnwrapNo (use regular swap)
Add LiquidityNo
Remove LiquidityNo
RWA swapsNo
Cross-chain bridgeNo

Important Details​

Token Requirements​

  • Gasless swaps require ERC-20 input tokens (not native USDC directly)
  • Native USDC is automatically converted to the ERC-20 representation for Permit2
  • The relayer never has access to your tokens — only the signed authorization

Nonce Management​

Each gasless swap uses a unique nonce combining:

  • Timestamp (for ordering)
  • Random component (for uniqueness)

This prevents replay attacks and ensures transactions are processed in order.

Deadline​

Gasless swaps have a 30-minute deadline. If the relayer cannot submit within this window, the signed authorization expires.

Relayer Retry Logic​

If the relayer encounters issues (nonce conflicts, network errors), it automatically:

  • Retries with different relayer wallets (up to 5 attempts)
  • Bumps gas fees progressively
  • Falls back to alternative RPC providers

Limits and Restrictions​

LimitValue
Max inputNo hard limit
Min input~0.000001 USDC equivalent
Deadline30 minutes
Custom recipientNot supported (sends to connected wallet only)
RWA swapsNot supported

Troubleshooting​

"Gasless swaps do not support native input"​

This error shouldn't occur — the UI automatically converts native USDC. If you see this, try refreshing the page.

"Permit2 not approved"​

Click Enable Permit2 for Gasless and confirm the approval in your wallet.

"Relayer request timed out"​

The relayer may be under heavy load. Try again in a few seconds, or disable gasless mode to swap normally.

"Transaction reverted"​

The swap conditions may have changed. Refresh the quote and try again with updated slippage settings.

Technical Details​

Contract Addresses​

ContractAddress
AchSwapGasless0x9f99094cA9e6516d4587E1A81952675D0a4d387A
Permit20x000000000022D473030F116dDEE9F6B43aC78BA3

Execution Kinds​

The relayer dispatches swaps based on protocol type:

KindProtocol
0Aggregator (split routing)
1V2
2V3 single-hop
3V3 multi-hop
4V4

EIP-712 Domain​

The gasless contract uses EIP-712 typed signatures:

  • Domain name: AchSwapGasless
  • Version: 1
  • Chain ID: 5042002 (ARC Testnet)
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