> ## Documentation Index
> Fetch the complete documentation index at: https://docs.overpass.ag/llms.txt
> Use this file to discover all available pages before exploring further.

# Build a swap transaction

> Build an unsigned versioned transaction from an Overpass quote.

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

```text theme={null}
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.

```ts theme={null}
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

```json theme={null}
{
  "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.

```ts theme={null}
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:

```json theme={null}
{
  "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.                         |