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

# simulateTransaction

> Simulate a Solana transaction to preview logs, compute-unit usage, and account changes without submitting it to the network.

Simulate a Solana transaction to preview logs, compute-unit usage, and account changes without submitting it to the network.

## On ThorNode

Forwarded to the upstream node with a 10 s timeout and one retry on a transport error. Runs on the upstream node's current state. Use `sigVerify: false` and `replaceRecentBlockhash: true` to simulate an unsigned or stale transaction, as in the example.

## Parameters

<ParamField body="transaction" type="string" required>
  The signed transaction, as an encoded string (base58 or base64).
</ParamField>

<ParamField body="encoding" type="string">
  Encoding used for the transaction data.

  * `base58`
  * `base64`
</ParamField>

<ParamField body="skipPreflight" type="boolean">
  Skip the preflight transaction checks.
</ParamField>

<ParamField body="preflightCommitment" type="string">
  Commitment level to use for preflight.

  * `confirmed`
  * `finalized`
  * `processed`
</ParamField>

<ParamField body="sigVerify" type="boolean">
  If true, verify the transaction signatures.
</ParamField>

<ParamField body="replaceRecentBlockhash" type="boolean">
  If true, replace the transaction recent blockhash with the most recent one.
</ParamField>

<ParamField body="minContextSlot" type="number">
  Minimum slot at which to perform preflight transaction checks.
</ParamField>

<ParamField body="innerInstructions" type="boolean">
  If true, include inner instructions in the response.
</ParamField>

<ParamField body="accounts" type="object" />

<ParamField body="accounts.addresses" type="array">
  Array of accounts to return, as base-58 encoded strings.
</ParamField>

<ParamField body="accounts.encoding" type="string">
  Encoding format for returned account data.

  * `base64`
  * `base58`
  * `base64+zstd`
  * `jsonParsed`
</ParamField>

## Response

<ResponseField name="context" type="object">
  Context of the simulation response.

  <Expandable title="properties">
    <ResponseField name="apiVersion" type="string">
      The API version of the RPC node.
    </ResponseField>

    <ResponseField name="slot" type="integer">
      Slot in which the data was fetched.
    </ResponseField>
  </Expandable>
</ResponseField>

<ResponseField name="value" type="object">
  Details of the simulated transaction result.

  <Expandable title="properties">
    <ResponseField name="accounts" type="array | null" />

    <ResponseField name="err" type="object | null">
      Error if the transaction failed, null if successful.
    </ResponseField>

    <ResponseField name="innerInstructions" type="array | null">
      Inner instructions executed during the transaction.
    </ResponseField>

    <ResponseField name="loadedAccountsDataSize" type="integer | null">
      Total size in bytes of all account data loaded during simulation.
    </ResponseField>

    <ResponseField name="logs" type="array | null">
      Program execution logs from the transaction simulation.
    </ResponseField>

    <ResponseField name="replacementBlockhash" type="object | null">
      Replacement blockhash information when replaceRecentBlockhash is enabled.

      <Expandable title="properties">
        <ResponseField name="blockhash" type="string">
          The replacement blockhash.
        </ResponseField>

        <ResponseField name="lastValidBlockHeight" type="integer">
          The last valid block height for the replacement blockhash.
        </ResponseField>
      </Expandable>
    </ResponseField>

    <ResponseField name="returnData" type="object | null">
      Data returned by the transaction if any.

      <Expandable title="properties">
        <ResponseField name="programId" type="string" />

        <ResponseField name="data" type="string[]" />
      </Expandable>
    </ResponseField>

    <ResponseField name="unitsConsumed" type="integer | null">
      Total compute units consumed during the simulation.
    </ResponseField>
  </Expandable>
</ResponseField>

<RequestExample>
  ```bash cURL theme={null}
  curl --fail-with-body "$THORNODE_RPC_URL" \
    --header 'content-type: application/json' \
    --data '{
      "jsonrpc": "2.0",
      "id": 1,
      "method": "simulateTransaction",
      "params": [
        "<BASE64_TRANSACTION>",
        {
          "encoding": "base64",
          "sigVerify": false,
          "replaceRecentBlockhash": true
        }
      ]
    }'
  ```

  ```javascript Node.js theme={null}
  const body = {
    "jsonrpc": "2.0",
    "id": 1,
    "method": "simulateTransaction",
    "params": [
      "<BASE64_TRANSACTION>",
      {
        "encoding": "base64",
        "sigVerify": false,
        "replaceRecentBlockhash": true
      }
    ]
  };

  const response = await fetch(process.env.THORNODE_RPC_URL, {
    method: "POST",
    headers: { "content-type": "application/json" },
    body: JSON.stringify(body),
  });
  const { result, error } = await response.json();
  console.log(result ?? error);
  ```
</RequestExample>

<ResponseExample>
  ```json Response theme={null}
  {
    "jsonrpc": "2.0",
    "result": {
      "context": {
        "apiVersion": "4.1.2",
        "slot": 439749205
      },
      "value": {
        "accounts": null,
        "err": null,
        "fee": 5000,
        "innerInstructions": null,
        "loadedAccountsDataSize": 149,
        "loadedAddresses": {
          "readonly": [],
          "writable": []
        },
        "logs": [
          "Program 11111111111111111111111111111111 invoke [1]",
          "Program 11111111111111111111111111111111 success"
        ],
        "postBalances": [
          777131893034520,
          1
        ],
        "postTokenBalances": [],
        "preBalances": [
          777131893039520,
          1
        ],
        "preTokenBalances": [],
        "replacementBlockhash": {
          "blockhash": "7T6Zk3mmgYodW6HNGYemPFYGAUNdyN25NgSefiRfCASH",
          "lastValidBlockHeight": 417799916
        },
        "returnData": null,
        "unitsConsumed": 150
      }
    },
    "id": 1
  }
  ```
</ResponseExample>