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simulateTransaction

Simulates sending a transaction. This performs all the same checks as sendTransaction (signature verification, balance checks, program execution) without actually submitting the transaction to the cluster. It returns the execution result including logs, compute units consumed, and any errors. This is invaluable for transaction debugging, fee estimation, validating transaction construction, and pre-flight checks before committing real transactions.

Parameters

#TypeRequiredDescription
1stringYesTransaction as an encoded string. Must be base-64 encoded
2objectNoConfiguration object

Configuration object fields:

FieldTypeDescription
commitmentstringCommitment level: processed, confirmed, or finalized
encodingstringEncoding of the transaction: base64 (default base64)
sigVerifyboolIf true, verify transaction signatures (default false; conflicts with replaceRecentBlockhash)
replaceRecentBlockhashboolIf true, replace the transaction's blockhash with the latest (default false)
accountsobjectAccounts configuration: { addresses: string[], encoding: string }
minContextSlotnumberMinimum slot at which the request can be evaluated
innerInstructionsboolIf true, include inner instructions in the response

Response

Returns an RpcResponse object:

FieldTypeDescription
context.slotu64The slot at which the simulation was evaluated
value.err`objectnull`
value.logs`array[string]null`
value.accounts`arraynull`
value.unitsConsumedu64Number of compute units consumed during simulation
value.returnData`objectnull`

Code Examples

cURL

Terminal
curl http://88.216.36.108:7999 -X POST -H "Content-Type: application/json" -d '{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "simulateTransaction",
  "params": [
    "AQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABAAEDArczbMia1tLmq7zz4DinMNN0pJ1JtLdqIJPUw3YrGCzYAMHBsgN27lcgB6H2WQvFgyZuJYHa46puOQo9yQ8CVQbd9uHXZaGT2cvhRs7reawctIXtX1s3kTqM9YV+/wCp20C7Wj2aiuk2TIQ0/jAgPDtfEP82jE2NpNsAACAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABSbxFRHKFUzK0X+2KniPE+eNjjVy10Ezz0o5/SCCr73AQIAAQA=",
    {
      "encoding": "base64",
      "replaceRecentBlockhash": true
    }
  ]
}'

TypeScript

TypeScript
const response = await fetch("http://88.216.36.108:7999", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    jsonrpc: "2.0",
    id: 1,
    method: "simulateTransaction",
    params: [
      "AQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABAAEDArczbMia1tLmq7zz4DinMNN0pJ1JtLdqIJPUw3YrGCzYAMHBsgN27lcgB6H2WQvFgyZuJYHa46puOQo9yQ8CVQbd9uHXZaGT2cvhRs7reawctIXtX1s3kTqM9YV+/wCp20C7Wj2aiuk2TIQ0/jAgPDtfEP82jE2NpNsAACAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABSbxFRHKFUzK0X+2KniPE+eNjjVy10Ezz0o5/SCCr73AQIAAQA=",
      {
        encoding: "base64",
        replaceRecentBlockhash: true
      }
    ]
  }),
});
const { result } = await response.json();
console.log("Simulation:", result.value.err ? "Failed" : "Success", "CU:", result.value.unitsConsumed);

Python

Python
import requests

response = requests.post("http://88.216.36.108:7999", json={
    "jsonrpc": "2.0",
    "id": 1,
    "method": "simulateTransaction",
    "params": [
        "AQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABAAEDArczbMia1tLmq7zz4DinMNN0pJ1JtLdqIJPUw3YrGCzYAMHBsgN27lcgB6H2WQvFgyZuJYHa46puOQo9yQ8CVQbd9uHXZaGT2cvhRs7reawctIXtX1s3kTqM9YV+/wCp20C7Wj2aiuk2TIQ0/jAgPDtfEP82jE2NpNsAACAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABSbxFRHKFUzK0X+2KniPE+eNjjVy10Ezz0o5/SCCr73AQIAAQA=",
        {
            "encoding": "base64",
            "replaceRecentBlockhash": True
        }
    ]
})
result = response.json()["result"]
print(f"Simulation: {'Failed' if result['value']['err'] else 'Success'}, CU: {result['value']['unitsConsumed']}")

Rust

Rust
use reqwest::Client;
use serde_json::json;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = Client::new();
    let res = client.post("http://88.216.36.108:7999")
        .json(&json!({
            "jsonrpc": "2.0",
            "id": 1,
            "method": "simulateTransaction",
            "params": [
                "AQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABAAEDArczbMia1tLmq7zz4DinMNN0pJ1JtLdqIJPUw3YrGCzYAMHBsgN27lcgB6H2WQvFgyZuJYHa46puOQo9yQ8CVQbd9uHXZaGT2cvhRs7reawctIXtX1s3kTqM9YV+/wCp20C7Wj2aiuk2TIQ0/jAgPDtfEP82jE2NpNsAACAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABSbxFRHKFUzK0X+2KniPE+eNjjVy10Ezz0o5/SCCr73AQIAAQA=",
                {
                    "encoding": "base64",
                    "replaceRecentBlockhash": true
                }
            ]
        }))
        .send().await?
        .text().await?;
    println!("{}", res);
    Ok(())
}

Example Response

JSON
{
  "jsonrpc": "2.0",
  "result": {
    "context": { "slot": 166974442 },
    "value": {
      "err": null,
      "logs": [
        "Program 11111111111111111111111111111111 invoke [1]",
        "Program 11111111111111111111111111111111 success"
      ],
      "accounts": null,
      "unitsConsumed": 150,
      "returnData": null
    }
  },
  "id": 1
}