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

#	Type	Required	Description
1	`string`	Yes	Transaction as an encoded string. Must be base-64 encoded
2	`object`	No	Configuration object

Configuration object fields:

Field	Type	Description
`commitment`	`string`	Commitment level: `processed`, `confirmed`, or `finalized`
`encoding`	`string`	Encoding of the transaction: `base64` (default `base64`)
`sigVerify`	`bool`	If `true`, verify transaction signatures (default `false`; conflicts with `replaceRecentBlockhash`)
`replaceRecentBlockhash`	`bool`	If `true`, replace the transaction's blockhash with the latest (default `false`)
`accounts`	`object`	Accounts configuration: `{ addresses: string[], encoding: string }`
`minContextSlot`	`number`	Minimum slot at which the request can be evaluated
`innerInstructions`	`bool`	If `true`, include inner instructions in the response

Response

Returns an RpcResponse object:

Field	Type	Description
`context.slot`	`u64`	The slot at which the simulation was evaluated
`value.err`	`object	null`
`value.logs`	`array[string]	null`
`value.accounts`	`array	null`
`value.unitsConsumed`	`u64`	Number of compute units consumed during simulation
`value.returnData`	`object	null`

Code Examples

cURL

1curl http://[IP_ADDRESS]:[PORT] -X POST -H "Content-Type: application/json" -d '{
2  "jsonrpc": "2.0",
3  "id": 1,
4  "method": "simulateTransaction",
5  "params": [
6    "AQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABAAEDArczbMia1tLmq7zz4DinMNN0pJ1JtLdqIJPUw3YrGCzYAMHBsgN27lcgB6H2WQvFgyZuJYHa46puOQo9yQ8CVQbd9uHXZaGT2cvhRs7reawctIXtX1s3kTqM9YV+/wCp20C7Wj2aiuk2TIQ0/jAgPDtfEP82jE2NpNsAACAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABSbxFRHKFUzK0X+2KniPE+eNjjVy10Ezz0o5/SCCr73AQIAAQA=",
7    {
8      "encoding": "base64",
9      "replaceRecentBlockhash": true
10    }
11  ]
12}'

TypeScript

1const response = await fetch("http://[IP_ADDRESS]:[PORT]", {
2  method: "POST",
3  headers: { "Content-Type": "application/json" },
4  body: JSON.stringify({
5    jsonrpc: "2.0",
6    id: 1,
7    method: "simulateTransaction",
8    params: [
9      "AQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABAAEDArczbMia1tLmq7zz4DinMNN0pJ1JtLdqIJPUw3YrGCzYAMHBsgN27lcgB6H2WQvFgyZuJYHa46puOQo9yQ8CVQbd9uHXZaGT2cvhRs7reawctIXtX1s3kTqM9YV+/wCp20C7Wj2aiuk2TIQ0/jAgPDtfEP82jE2NpNsAACAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABSbxFRHKFUzK0X+2KniPE+eNjjVy10Ezz0o5/SCCr73AQIAAQA=",
10      {
11        encoding: "base64",
12        replaceRecentBlockhash: true
13      }
14    ]
15  }),
16});
17const { result } = await response.json();
18console.log("Simulation:", result.value.err ? "Failed" : "Success", "CU:", result.value.unitsConsumed);

Python

1import requests
2
3response = requests.post("http://[IP_ADDRESS]:[PORT]", json={
4    "jsonrpc": "2.0",
5    "id": 1,
6    "method": "simulateTransaction",
7    "params": [
8        "AQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABAAEDArczbMia1tLmq7zz4DinMNN0pJ1JtLdqIJPUw3YrGCzYAMHBsgN27lcgB6H2WQvFgyZuJYHa46puOQo9yQ8CVQbd9uHXZaGT2cvhRs7reawctIXtX1s3kTqM9YV+/wCp20C7Wj2aiuk2TIQ0/jAgPDtfEP82jE2NpNsAACAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABSbxFRHKFUzK0X+2KniPE+eNjjVy10Ezz0o5/SCCr73AQIAAQA=",
9        {
10            "encoding": "base64",
11            "replaceRecentBlockhash": True
12        }
13    ]
14})
15result = response.json()["result"]
16print(f"Simulation: {'Failed' if result['value']['err'] else 'Success'}, CU: {result['value']['unitsConsumed']}")

Rust

1use reqwest::Client;
2use serde_json::json;
3
4#[tokio::main]
5async fn main() -> Result<(), Box<dyn std::error::Error>> {
6    let client = Client::new();
7    let res = client.post("http://[IP_ADDRESS]:[PORT]")
8        .json(&json!({
9            "jsonrpc": "2.0",
10            "id": 1,
11            "method": "simulateTransaction",
12            "params": [
13                "AQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABAAEDArczbMia1tLmq7zz4DinMNN0pJ1JtLdqIJPUw3YrGCzYAMHBsgN27lcgB6H2WQvFgyZuJYHa46puOQo9yQ8CVQbd9uHXZaGT2cvhRs7reawctIXtX1s3kTqM9YV+/wCp20C7Wj2aiuk2TIQ0/jAgPDtfEP82jE2NpNsAACAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABSbxFRHKFUzK0X+2KniPE+eNjjVy10Ezz0o5/SCCr73AQIAAQA=",
14                {
15                    "encoding": "base64",
16                    "replaceRecentBlockhash": true
17                }
18            ]
19        }))
20        .send().await?
21        .text().await?;
22    println!("{}", res);
23    Ok(())
24}

Example Response

1{
2  "jsonrpc": "2.0",
3  "result": {
4    "context": { "slot": 166974442 },
5    "value": {
6      "err": null,
7      "logs": [
8        "Program 11111111111111111111111111111111 invoke [1]",
9        "Program 11111111111111111111111111111111 success"
10      ],
11      "accounts": null,
12      "unitsConsumed": 150,
13      "returnData": null
14    }
15  },
16  "id": 1
17}