> For the complete documentation index, see [llms.txt](https://docs.fynd.xyz/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.fynd.xyz/guides/client-fees.md). # Charge Fees on your Swaps Use client fees to monetize your swap flow. Client fees are optional integrator fees set with `ClientFeeParams`. The integrator keeps 80% of the client fee. Fynd keeps 20%. Client fees are separate from [Fynd fees](/guides/router-fees.md), which still apply when no client fee is set. ## Fee breakdown with client fees Quotes with encoding include a `fee_breakdown` with the exact amounts. `amount_out` is the raw pre-fee swap output: what the route produces before router or client fees. It is **not** what the user receives. The user receives at least `fee_breakdown.min_amount_received` on-chain. Fynd mirrors the on-chain `FeeCalculator` with identical integer arithmetic, then uses the result for `minAmountOut` in the encoded transaction. Given `amount_out`, `router_fee_bps` (see [Fynd Fees](/guides/router-fees.md)), `client_fee_bps`, and `slippage`: ``` 1. client_fee = amount_out * client_fee_bps / 10,000 2. router_share = amount_out * client_fee_bps * 2,000 / 100,000,000 3. client_portion = client_fee - router_share 4. router_fee_output = amount_out * router_fee_bps / 10,000 5. router_fee = router_share + router_fee_output 6. amount_after_fees = amount_out - client_portion - router_fee 7. max_slippage = amount_after_fees * slippage 8. min_amount_received = amount_after_fees - max_slippage ``` All response fields use output token units: | Field | Description | | --------------------- | ------------------------------------------------------------- | | `router_fee` | Fynd fee + 20% of client fee | | `client_fee` | Integrator's 80% share of the client fee | | `max_slippage` | Slippage allowance on the post-fee amount | | `min_amount_received` | On-chain minimum the user receives (`minAmountOut` in the tx) | Invariant: `amount_out = router_fee + client_fee + max_slippage + min_amount_received` ### Example Example: 1,000,000 USDC output, 0.1 bps Fynd fee, 50 bps client fee, 1% slippage: ``` client_fee (total) = 1,000,000 * 50 / 10,000 = 5,000 router_share = 1,000,000 * 50 * 2,000 / 1e8 = 1,000 client_portion = 5,000 - 1,000 = 4,000 router_fee_output = 1,000,000 * 0.1 / 10,000 = 10 router_fee = 10 + 1,000 = 1,010 amount_after_fees = 1,000,000 - 4,000 - 1,010 = 994,990 max_slippage = 994,990 * 0.01 = 9,949 min_amount_received = 994,990 - 9,949 = 985,041 ``` ## Setting up client fees 1. Set a fee in basis points (e.g. `50` = 0.5%), a receiver address, and a `maxClientContribution`. 2. Have the fee receiver sign an EIP-712 `ClientFee` message authorizing these parameters. 3. Attach the signed params to `EncodingOptions.clientFeeParams`. 4. The router verifies the signature on-chain and deducts the fee. Fees go to the receiver's vault balance. Without `ClientFeeParams`, no client fee is charged. [Fynd fees](/guides/router-fees.md) still apply. ### maxClientContribution `maxClientContribution` caps how much the client can subsidize from their vault balance if slippage pushes the output below `minAmountOut`. If the shortfall exceeds the cap, the transaction reverts. Set it to `0` to collect fees without covering slippage losses. This is the common case. See [Tycho encoding docs](https://docs.propellerheads.xyz/tycho/for-solvers/execution/encoding#encode) for vault details. ## EIP-712 signing The fee receiver signs a typed data hash: | Field | Type | Description | | ----------------------- | --------- | --------------------------------- | | `clientFeeBps` | `uint16` | Fee in basis points (0-10,000) | | `clientFeeReceiver` | `address` | Address receiving the fee | | `maxClientContribution` | `uint256` | Maximum subsidy from client vault | | `deadline` | `uint256` | Signature expiry (Unix timestamp) | **EIP-712 domain:** | Field | Value | | ------------------- | ---------------------------- | | `name` | `TychoRouter` | | `version` | `1` | | `chainId` | Target chain ID | | `verifyingContract` | TychoRouter contract address | ## Code examples {% tabs %} {% tab title="TypeScript" %} ```typescript // Build fee params (without signature). const feeParams: ClientFeeParams = { bps: 50, // 0.5% fee receiver: feeReceiver, maxContribution: 0n, // no vault subsidy deadline: 1893456000, // Unix timestamp }; // Compute the EIP-712 hash and sign with the fee receiver's wallet. const hash = clientFeeSigningHash(feeParams, 1, routerAddress); const signature = await account.signMessage({message: {raw: hash}}); // Attach signature and wire into encoding options. const opts = withClientFee(encodingOptions(0.005), {...feeParams, signature}); ``` {% endtab %} {% tab title="Rust" %} ```rust // Step 1: request a quote using unsigned client fee params. // The server encodes the full calldata and returns `swaps_hash` // in the fee breakdown and `signature_offset` in the transaction // so the client can patch the real signature in. let fee = ClientFeeParams::new( FEE_BPS, Bytes::copy_from_slice(fee_receiver.as_slice()), BigUint::ZERO, u64::MAX, ); let order = Order::new( Bytes::copy_from_slice(sell_token.as_slice()), Bytes::copy_from_slice(buy_token.as_slice()), BigUint::from(SELL_AMOUNT), OrderSide::Sell, Bytes::copy_from_slice(sender.as_slice()), None, ); let quote = client .quote(QuoteParams::new( order, QuoteOptions::default() .with_timeout_ms(5_000) .with_encoding_options(EncodingOptions::new(SLIPPAGE).with_client_fee(fee.clone())), )) .await?; let fee_breakdown = quote .fee_breakdown() .ok_or("no fee breakdown in quote")?; let swaps_hash = fee_breakdown .swaps_hash() .ok_or("no swaps_hash — server must support client fee signing")?; // Step 2: sign the full 10-field EIP-712 ClientFee hash. // receiver defaults to sender when the order has no explicit receiver. let hash = fee.eip712_signing_hash( chain_id, &router_address, quote.amount_in(), &Bytes::copy_from_slice(sell_token.as_slice()), &Bytes::copy_from_slice(buy_token.as_slice()), fee_breakdown.min_amount_received(), &Bytes::copy_from_slice(sender.as_slice()), swaps_hash, )?; let sig = fee_signer .sign_hash(&B256::from(hash)) .await?; // Step 3: patch the real signature into the calldata. let quote = quote.with_client_fee_signature(&sig.as_bytes()[..])?; ``` See the full working example: [`clients/rust/examples/swap_client_fee.rs`](https://github.com/propeller-heads/fynd/blob/main/clients/rust/examples/swap_client_fee.rs) {% endtab %} {% endtabs %} --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.fynd.xyz/guides/client-fees.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.