Build a swap transaction

Build an unsigned Solana versioned transaction from an Overpass exact-in quote.

POST https://api-v1.overpass.ag/v1/swap

The transaction deposits an underlying asset and mints the yield token, or burns the yield token and withdraws the underlying asset. The direction comes from the quote’s mint pair.

Request body

Field	Type	Required	Description
`userPublicKey`	string	Yes	Wallet that signs and pays for the transaction.
`quoteResponse`	object	Conditional	Complete response returned by `GET /v1/quote`. Required unless `inputMint`, `outputMint`, and `amount` are supplied directly.
`priorityFeeMicroLamports`	integer	No	Compute-unit price in micro-lamports. Defaults to `0`.
`computeUnitLimit`	integer	No	Explicit compute-unit limit. The API otherwise uses the builder’s suggested limit.

Pass the quote response unchanged. This preserves the quote’s otherAmountThreshold as the minimum acceptable output.

const response = await fetch("https://api-v1.overpass.ag/v1/swap", {
  method: "POST",
  headers: {
    "content-type": "application/json",
  },
  body: JSON.stringify({
    userPublicKey: wallet.publicKey.toBase58(),
    quoteResponse,
  }),
});

if (!response.ok) {
  const error = await response.json();
  throw new Error(error.message ?? error.error);
}

const swap = await response.json();

Response

{
  "swapTransaction": "AQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA...",
  "lastValidBlockHeight": 409970749,
  "prioritizationFeeLamports": 0,
  "priorityFeeMicroLamports": 0,
  "computeUnitLimit": 430000,
  "swapMode": "ExactIn",
  "txVersion": "V0",
  "quoteResponse": {
    "inputMint": "So11111111111111111111111111111111111111112",
    "inAmount": "10000000",
    "outputMint": "HtnnuzVtecjktsUoZjHaZoZ9u4jPAzGpujE82U3v3cAV",
    "outAmount": "9922552",
    "otherAmountThreshold": "9872939",
    "swapMode": "ExactIn",
    "slippageBps": 50,
    "platformFee": null,
    "priceImpactPct": "0",
    "routePlan": [
      {
        "swapInfo": {
          "ammKey": "9iJeZPrNJrBEjj4h7tD9P3hygyM4hpZmyqrQmHjNUpdA",
          "label": "Overpass kamino",
          "inputMint": "So11111111111111111111111111111111111111112",
          "outputMint": "HtnnuzVtecjktsUoZjHaZoZ9u4jPAzGpujE82U3v3cAV",
          "inAmount": "10000000",
          "outAmount": "9922552",
          "feeAmount": "0",
          "feeMint": "So11111111111111111111111111111111111111112"
        },
        "percent": 100
      }
    ],
    "contextSlot": 431902057,
    "timeTaken": 0.029,
    "wrapperMint": "HtnnuzVtecjktsUoZjHaZoZ9u4jPAzGpujE82U3v3cAV",
    "wrapperVault": "9iJeZPrNJrBEjj4h7tD9P3hygyM4hpZmyqrQmHjNUpdA",
    "underlyingMint": "So11111111111111111111111111111111111111112",
    "sourcePool": "HaVsdBb4mMoYQ3vnS7wCdvhixg5xFQALmFwyL9QJm3fn",
    "protocol": "kamino",
    "direction": "deposit",
    "protocolDepositFeeBps": 0,
    "creatorDepositFeeBps": 0,
    "warnings": []
  }
}

Field	Description
`swapTransaction`	Base64-encoded unsigned versioned transaction.
`lastValidBlockHeight`	Last block height at which the transaction remains valid.
`prioritizationFeeLamports`	Total priority fee implied by the compute limit and compute-unit price.
`priorityFeeMicroLamports`	Compute-unit price included in the transaction.
`computeUnitLimit`	Compute-unit limit included in the transaction.
`txVersion`	Transaction version. Overpass returns `V0`.
`quoteResponse`	Fresh quote used to build the transaction.

Sign and send

Deserialize the transaction, ask the wallet to sign it, and submit the signed bytes through your Solana connection.

import { Connection, VersionedTransaction } from "@solana/web3.js";

const connection = new Connection(SOLANA_RPC_URL, "confirmed");
const transaction = VersionedTransaction.deserialize(
  Uint8Array.from(globalThis.atob(swap.swapTransaction), (character) =>
    character.charCodeAt(0),
  ),
);

const simulation = await connection.simulateTransaction(transaction, {
  sigVerify: false,
});

if (simulation.value.err) {
  throw new Error(`Simulation failed: ${JSON.stringify(simulation.value.err)}`);
}

const signed = await wallet.signTransaction(transaction);
const signature = await connection.sendRawTransaction(signed.serialize(), {
  skipPreflight: false,
  maxRetries: 3,
});

await connection.confirmTransaction(
  {
    signature,
    blockhash: transaction.message.recentBlockhash,
    lastValidBlockHeight: swap.lastValidBlockHeight,
  },
  "confirmed",
);

Request a new quote and transaction when the block height expires or when execution fails because source-pool state changed.

Direct request

You can build a transaction without sending a prior quote response by providing the route fields directly:

{
  "userPublicKey": "BQ72nSv9f3PRyRKCBnHLVrerrv37CYTHm5h3s9VSGQDV",
  "inputMint": "So11111111111111111111111111111111111111112",
  "outputMint": "HtnnuzVtecjktsUoZjHaZoZ9u4jPAzGpujE82U3v3cAV",
  "amount": "10000000",
  "slippageBps": 50,
  "swapMode": "ExactIn"
}

The API computes a fresh quote before building the transaction. Use the quote-first flow when you need to display the expected output, fees, or warnings before execution.

Errors

Swap errors use the same { "error", "message" } shape as the quote endpoint.

Status	Meaning
`400`	Missing quote fields, invalid wallet, amount, slippage, or swap mode.
`404`	No Overpass wrapper route exists for the mint pair.
`422`	The route could not be quoted or built.
`429`	The request exceeded the API rate limit.
`503`	Current source-protocol state is unavailable.

Start here

Overpass API

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Reference

Build a swap transaction

Request body

Response

Sign and send

Direct request

Errors

​Request body

​Response

​Sign and send

​Direct request

​Errors

Request body

Response

Sign and send

Direct request

Errors