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Protocol Fees

Hyperbridge charges a non-refundable protocol fee per byte of the request/response body. This fee is withdrawn from the contract account calling the IsmpDispatcher. Importantly, the contract must first approve the EvmHost to withdraw the exact amount before calling the dispatch function.

Expected Workflow:

Contracts initiating a dispatch should:

  • Withdraw the protocol fee from the user's account.
  • Grant the EvmHost approval to withdraw the same amount.
  • Call the dispatch function on the host.

Finding the Fee Token:

The token accepted for protocol fee payments is readily available through IIsmpHost(_host).feeToken().

The following snippet shows how to calculate the protocol fee for a post request.

    import {IIsmpHost} from "ismp/IIsmpHost.sol";
    // _host is variable that contains the EvmHost contract address
    abstract contract Example {
        function hyperbridgeFee(bytes memory body) external view returns (uint256) {
            memory perByteFee = IIsmpHost(_host).perByteFee();
            uint256 protocolFee = perByteFee * body.length;
            return protocolFee;
        function feeToken() external view returns (address) {
            return IIsmpHost(_host).feeToken()

In the case of Post responses the protocol fee is calculated from the size of the response.

Hyperbridge Relayer Fees

The relayer fee is an optional incentive provided by users initiating cross-chain transactions. It compensates Hyperbridge's decentralized relayers for delivering messages to the destination chain.


The fee consists of two parts:

  • Gas fee: This covers the cost of executing the message on the destination chain.
  • Relayer service fee: This additional amount rewards relayers for their services. Relayers are profit-Driven mediators and they will prioritize messages with fees that ensure profitability.

Setting the Fee

To account for potential gas price fluctuations during message delivery, consider the following:

  • Proof verification cost: For a cross-chain message to be delivered and executed, it must first be authenticated through state proofs. The expected cost for state proof verification is 120k gas. Contracts should account for the stablecoin equivalent cost when setting the relayer fee.
  • Message execution gas cost: The usd equivalent for the gas cost of executing the message
  • Gas price buffer: Include a buffer to accommodate gas price spikes.
  • Relayer service charge: Factor in a reasonable amount to compensate relayers.
  • Self-Relay Option: Users can choose to self-relay messages by omitting the relayer fee.

Collecting Relayer Fees

If a user provides a non-zero relayer fee, then the contract should withdraw the fee from the user's account. When the contract calls dispatch, the EvmHost will attempt to withdraw the relayer fee from the contract's account. Ensure the contract approves the EvmHost for the amount specified as the relayer fee before calling dispatch.

Mitigating Gas Cost Spikes

During periods of high gas prices on the destination chain, you can increase the relayer fee for in-flight requests and responses to incentivize their delivery. The EvmHost contract provides the fundRequest and fundResponse functions for this purpose. Simply call the appropriate function with the request/response commitment and the desired fee increase amount.