Swap Trading¶

Swaps provide instant execution for traders who want to exchange tokens immediately at the best available price. Unlike limit orders, swaps are Fill-or-Kill — they either execute in full or are rejected.

Swap Flow¶

sequenceDiagram
    participant User
    participant API as Sera API
    participant Chain as Ethereum

    User->>API: POST /swap/quote
    API-->>User: Quote (uuid, route_params)
    User->>User: Sign route_params (EIP-712)
    User->>API: POST /swap (uuid + signature)
    API->>Chain: Settlement
    Chain-->>API: Confirmation
    API-->>User: Success (trade_id)

Step 1: Request a Quote¶

const response = await fetch('https://api.sera.cx/api/v1/swap/quote', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    from_token: '0xDcAE...285b',  // USDC address
    to_token: '0xd3Bd...779',     // EURC address
    from_amount: '1000000000',    // 1000 USDC (6 decimals)
    owner_address: '0xYOUR_WALLET',
    recipient: '0xYOUR_WALLET',   // Where to receive output (may be a different address)
    expiration: Math.floor(Date.now() / 1000) + 3600,  // 1 hour
    gas_mode: 'receive_less'
  })
});

const quote = await response.json();
// quote.uuid — Unique quote identifier
// quote.route_params — EIP-712 parameters to sign
// quote.fee_breakdown — Gas cost details (gas_cost_usd, gas_cost_from_token)

POST /swap atomically consumes the stored quote on the first valid submission. If execution fails after the quote is consumed, request a new quote instead of retrying the same uuid.

Quote Parameters¶

Quote Response¶

The response includes:

• uuid — A unique identifier for this quote (used when submitting)
• route_params — The EIP-712 Intent struct fields to sign
• fee_breakdown — Gas cost details: gas_cost_usd and gas_cost_from_token
• expires_at — When the quote expires (quotes are one-time use)

Step 2: Sign the Quote¶

Sign the route_params using EIP-712 typed data signing with your wallet:

import { ethers } from 'ethers';

// The EIP-712 domain
const domain = {
  name: 'Sera',
  version: '1',
  chainId: 11155111,  // Sepolia
  verifyingContract: '0xd0fc92d8eF9bE26D7288fCa1D6458f675e72B83a'  // Sera.sol
};

// The Intent type
const types = {
  Intent: [
    { name: 'taker', type: 'address' },
    { name: 'inputToken', type: 'address' },
    { name: 'outputToken', type: 'address' },
    { name: 'maxInputAmount', type: 'uint256' },
    { name: 'minOutputAmount', type: 'uint256' },
    { name: 'recipient', type: 'address' },
    { name: 'initialDepositAmount', type: 'uint256' },
    { name: 'uuid', type: 'uint256' },
    { name: 'deadline', type: 'uint48' },
  ]
};

// Sign quote.route_params exactly as returned by POST /swap/quote
const signature = await signer.signTypedData(domain, types, quote.route_params);

Step 3: Execute the Swap¶

Submit the signed quote:

const result = await fetch('https://api.sera.cx/api/v1/swap', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    uuid: quote.uuid,
    signature: signature
  })
});

const swap = await result.json();
// swap.success — Whether the swap was accepted
// swap.trade_id — Unique trade identifier for tracking

Gas Modes¶

Unlike limit orders (where you pay gas in real ETH), swap gas costs are automatically factored into the quote by the server. You do not need to hold ETH to execute a swap — the gas is absorbed into the token amounts.

When requesting a quote, you choose how the gas cost is applied:

The fee_breakdown in the quote response shows the exact gas cost so there are no surprises. The server computes the adjusted amounts — your frontend simply signs the route_params as-is.

When the Markup Is Skipped¶

The 0.1% cross-currency markup is dropped in two cases:

• Same-currency swaps between two pegs of the same fiat currency — for example USDC↔USDT, or two SGD-denominated stablecoins. There is no FX exposure to price in, and the two pegs typically cluster within a basis point of 1:1, so the quote prices straight off the orderbook (subject to the gas-mode adjustment you selected).
• When the orderbook beats the oracle for a cross-currency pair. Sera quotes the worse of the two prices for the user; when that turns out to be the oracle (i.e. the OB would have given you more), the platform already retains the OB-vs-oracle spread and does not charge an additional markup on top.

Multi-Leg Routing¶

Sera automatically finds optimal routes for your swap. If a direct pair doesn't exist or a multi-hop path offers better pricing, the swap routes through intermediate currencies transparently.

For example, a GBP → SGD swap might execute as:

1. GBP → USD
2. USD → SGD

This happens atomically — either all legs succeed or none do.

Why MEV Is Not an Issue¶

Sera swaps are not executed like public AMM swaps. Quote generation, routing, and matching happen off-chain in Sera's Web2 engine, and Ethereum is used only as the final settlement layer.

That means users are not exposing an open-ended market order to the public mempool for price discovery. Instead, you request a quote, sign the exact route_params, and settlement either executes within the signed bounds or fails.

The signed Intent includes maxInputAmount, minOutputAmount, a one-time uuid, and a deadline. Because the trade is not being discovered and repriced in the public mempool, the usual sandwich-attack vector does not exist.

Error Handling¶

Every 4xx response from POST /swap returns a typed envelope:

{
  "detail": {
    "detail": "Quote was rejected; request a fresh quote",
    "error_code": "QUOTE_STALE"
  }
}

Branch on error_code for routing logic; the inner detail is a human-readable string for display only. The full code list is documented in the Swap endpoints reference.