Initiating a Swap

This guide shows how to build and send a swap with the Mento SDK v3. The SDK returns transaction parameters (including an approval transaction if needed); you submit them with any viem wallet client.

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Create the client and get a quote

Read-only operations (quotes, routes) only need a public client. For building swap transactions you still use Mento.create; the SDK returns transaction parameters that you send with your own wallet:

import { Mento, ChainId, deadlineFromMinutes } from '@mento-protocol/mento-sdk'
import { parseUnits } from 'viem'

const mento = await Mento.create(ChainId.CELO)

const USDm = '0x765DE816845861e75A25fCA122bb6898B8B1282a'
const CELO = '0x471EcE3750Da237f93B8E339c536989b8978a438'
const amountIn = parseUnits('100', 18)

const expectedOut = await mento.quotes.getAmountOut(USDm, CELO, amountIn)

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Build swap transaction (approval + swap)

buildSwapTransaction returns both an approval (if the token needs an allowance) and the swap transaction. All public APIs use object-based parameters:

const recipientAddress = '0x...'  // address that receives the output tokens
const ownerAddress = '0x...'     // address that holds tokenIn and signs the tx

const { approval, swap } = await mento.swap.buildSwapTransaction(
  USDm,
  CELO,
  amountIn,
  recipientAddress,
  ownerAddress,
  {
    slippageTolerance: 0.5,           // 0.5%
    deadline: deadlineFromMinutes(5),
  }
)

• slippageTolerance — percentage (e.g. 0.5 = 0.5%). The SDK caps this (e.g. at 50%) to reduce sandwich risk.

• deadline — use deadlineFromMinutes(minutes) or pass a Unix timestamp.

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Send with a viem wallet client

Execute the approval first (if present), then the swap:

import { createWalletClient, custom } from 'viem'
import { celo } from 'viem/chains'

const walletClient = createWalletClient({
  chain: celo,
  transport: custom(window.ethereum),
})

if (approval) {
  await walletClient.sendTransaction(approval)
}
await walletClient.sendTransaction(swap.params)

The SDK returns transaction request objects; you are responsible for sending them and handling receipts (e.g. waiting for confirmation).

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Summary

1. Quote — mento.quotes.getAmountOut(tokenIn, tokenOut, amountIn) (or getAmountIn for exact amount out).

2. Build — mento.swap.buildSwapTransaction(tokenIn, tokenOut, amountIn, recipient, owner, { slippageTolerance, deadline }).

3. Send — If approval is set, send it first; then send swap.params with your viem wallet client.

Runnable examples: mento-sdk-examples.