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Version: 2.0

Understanding Gasless API

Description: Learn how 0x’s Gasless API works, including the terminology, mechanics, and how to implement gasless swaps and approvals in your app.

Why Use the Gasless API?​

In typical Web3 flows, users must pay gas fees using the network’s native token (e.g., ETH, POL) during:

  1. Token approval – granting a contract permission to spend tokens.
  2. Swap execution – submitting the swap transaction itself.

This requirement increases onboarding friction—especially for new users without native tokens. The Gasless API removes that hurdle by allowing a relayer (e.g., 0x) to cover gas costs. Users can then complete swaps without needing the native token in their wallet.

How It Works​

The Gasless API returns indicative prices and firm quotes for swaps. If the user accepts a quote, they sign an EIP-712 message authorizing:

  • A gasless token approval (if supported), and/or
  • The swap transaction itself.

0x then submits the signed data as a meta-transaction on-chain and pays the gas cost.

While “gasless” means no upfront gas from the user, gas is still consumed—just paid by a relayer like 0x. Gas fees are usually deducted from the input token (the token the user is selling).

Note: Gasless swaps work for all non-native ERC-20 tokens.

Supported Tokens​

Gasless functionality is split into two categories:

FeatureSupported Tokens
Gasless ApprovalsTokens that support EIP-2612. Check supported tokens via the API endpoint.
Gasless SwapsAny non-native ERC-20 token.

Key Concepts​

Token Allowances​

A token allowance lets a smart contract move a user’s tokens. For tokens that don’t support gasless approvals, the user must call approve() themselves (gasful). See how to set token allowances.

For gasless flows, the user signs an EIP-712 message instead of broadcasting a transaction.

EIP-712: Typed Message Signing​

EIP-712 enables human-readable signatures for structured data. Wallets can show users exactly what they're signing—crucial for both gasless approvals and gasless swaps.

EIP-2612: Gasless Approvals​

EIP-2612 adds a permit() method to ERC-20 tokens, allowing gasless approvals using an EIP-712 signature. This avoids needing an approve() transaction.

Permit2​

Permit2 is a smart contract by Uniswap that enables a universal allowance model:

  • Deployed to 0x000000000022D473030F116dDEE9F6B43aC78BA3 on all chains.
  • Users approve Permit2 once, and it can then authorize other contracts (like 0x’s Settler) to transfer tokens on their behalf using a signed EIP-712 message.
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What’s the difference between Permit (EIP-2612) and Permit2?

Gasless Approvals​

Supported if the token has permit() (EIP-2612). The user signs an EIP-712 message to grant allowance. This is possible for tokens that support the Permit Extension (EIP-2612).

Gasless Transactions​

User signs an EIP-712 message authorizing a swap. 0x pays gas and executes on-chain via metatransactions

Settler Metatransaction​

Metatransactions are messages that authorize smart contracts to perform actions on your behalf.

Settler Metatransactions, settler_metatransaction, represents a type of gasless transactions returned by the Gasless API /gasless/quote endpoint. Settler Metatransaction leverages the Swap API to fetch indicative pricing and quotes. 0x submits these transactions to the blockchain on behalf of the user.

WETH Example​

Let’s say the user wants to sell WETH:

  • WETH does not support EIP-2612, so gasless approvals are not possible.
  • However, gasless swaps are supported using an EIP-712 signature.
  • First, set a token allowance for WETH (this requires gas).
  • After Permit2 has spending permission, the user can sign an EIP-712 trade message to execute the swap without paying gas.

Technical Flow Diagrams​

The Gasless API can be combined with the Swap API to provide flexible execution options. This allows for a seamless user experience where advanced users can choose to enable or disable Gasless execution without compromising their experience:

  • Default to gasless trades when possible.
  • Fallback to regular Swap API when:
    • The token is native and unsupported for gasless.
    • There’s not enough input token to cover relayer gas costs.

Click to expand flowchart

Gasless + Swap API Flow

🔍 Try It Live​

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