> ## Documentation Index
> Fetch the complete documentation index at: https://www.helius.dev/docs/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 — used to estimate fees, detect failures, and debug instructions before signing.
## Request Parameters
The signed transaction, as an encoded string (base58 or base64).
Encoding used for the transaction data.
* `base58`
* `base64`
Skip the preflight transaction checks.
Commitment level to use for preflight.
* `confirmed`
* `finalized`
* `processed`
If true, verify the transaction signatures.
If true, replace the transaction recent blockhash with the most recent one.
Minimum slot at which to perform preflight transaction checks.
If true, include inner instructions in the response.
Array of accounts to return, as base-58 encoded strings.
Encoding format for returned account data.
* `base64`
* `base58`
* `base64+zstd`
* `jsonParsed`
## OpenAPI
````yaml openapi/rpc-http/simulateTransaction.yaml POST /
openapi: 3.1.0
info:
title: Solana RPC API
version: 1.0.0
description: >-
Advanced Solana transaction simulation API for testing and debugging
blockchain transactions before committing them to the Solana network.
license:
name: Apache 2.0
url: https://www.apache.org/licenses/LICENSE-2.0.html
servers:
- url: https://mainnet.helius-rpc.com
description: Mainnet RPC endpoint
- url: https://devnet.helius-rpc.com
description: Devnet RPC endpoint
security: []
paths:
/:
post:
tags:
- RPC
summary: simulateTransaction
description: >
Simulate Solana transactions without executing them on the blockchain.
This powerful
debugging tool allows developers to test transaction execution, verify
program behavior,
estimate compute unit consumption, detect errors, and preview account
state changes
before committing transactions to the network. Essential for Solana
application
development, smart contract testing, and transaction optimization.
operationId: simulateTransaction
requestBody:
required: true
content:
application/json:
schema:
type: object
properties:
jsonrpc:
type: string
enum:
- '2.0'
description: The JSON-RPC protocol version.
example: '2.0'
default: '2.0'
id:
type: string
description: A unique identifier for the request.
example: '1'
default: '1'
method:
type: string
enum:
- simulateTransaction
description: The name of the RPC method to invoke.
example: simulateTransaction
default: simulateTransaction
params:
type: array
description: Parameters for simulating a transaction.
default:
- >-
AQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABAAEDArczbMia1tLmq7zz4DinMNN0pJ1JtLdqIJPUw3YrGCzYAMHBsgN27lcgB6H2WQvFgyZuJYHa46puOQo9yQ8CVQbd9uHXZaGT2cvhRs7reawctIXtX1s3kTqM9YV+/wCp20C7Wj2aiuk5TReAXo+VTVg8QTHjs0UjNMMKCvpzZ+ABAgEBARU=
- encoding: base64
items:
oneOf:
- type: string
description: >-
The signed transaction, as an encoded string (base58
or base64).
example: >-
AQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABAAEDArczbMia1tLmq7zz4DinMNN0pJ1JtLdqIJPUw3YrGCzYAMHBsgN27lcgB6H2WQvFgyZuJYHa46puOQo9yQ8CVQbd9uHXZaGT2cvhRs7reawctIXtX1s3kTqM9YV+/wCp20C7Wj2aiuk5TReAXo+VTVg8QTHjs0UjNMMKCvpzZ+ABAgEBARU=
- type: object
description: Configuration object for the simulation.
properties:
encoding:
type: string
description: Encoding used for the transaction data.
enum:
- base58
- base64
example: base64
skipPreflight:
type: boolean
description: Skip the preflight transaction checks.
example: false
preflightCommitment:
type: string
description: Commitment level to use for preflight.
enum:
- confirmed
- finalized
- processed
example: finalized
sigVerify:
type: boolean
description: If true, verify the transaction signatures.
example: false
replaceRecentBlockhash:
type: boolean
description: >-
If true, replace the transaction recent blockhash
with the most recent one.
example: false
minContextSlot:
type: integer
description: >-
Minimum slot at which to perform preflight
transaction checks.
example: 1000
innerInstructions:
type: boolean
description: >-
If true, include inner instructions in the
response.
example: false
accounts:
type: object
properties:
addresses:
type: array
description: >-
Array of accounts to return, as base-58
encoded strings.
items:
type: string
example: 83astBRguLMdt2h5U1Tpdq5tjFoJ6noeGwaY3mDLVcri
encoding:
type: string
description: Encoding format for returned account data.
enum:
- base64
- base58
- base64+zstd
- jsonParsed
example: base64
example:
jsonrpc: '2.0'
id: '1'
method: simulateTransaction
params:
- >-
AQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABAAEDArczbMia1tLmq7zz4DinMNN0pJ1JtLdqIJPUw3YrGCzYAMHBsgN27lcgB6H2WQvFgyZuJYHa46puOQo9yQ8CVQbd9uHXZaGT2cvhRs7reawctIXtX1s3kTqM9YV+/wCp20C7Wj2aiuk5TReAXo+VTVg8QTHjs0UjNMMKCvpzZ+ABAgEBARU=
- encoding: base64
responses:
'200':
description: Successfully simulated the transaction.
content:
application/json:
schema:
type: object
properties:
jsonrpc:
type: string
description: The JSON-RPC protocol version.
enum:
- '2.0'
example: '2.0'
id:
type: string
description: Identifier matching the request.
example: '1'
result:
type: object
description: Result of the simulated transaction.
properties:
context:
type: object
description: Context of the simulation response.
properties:
apiVersion:
type: string
description: The API version of the RPC node.
example: 2.3.3
slot:
type: integer
description: Slot in which the data was fetched.
example: 393226680
value:
type: object
description: Details of the simulated transaction result.
properties:
accounts:
type:
- array
- 'null'
items:
type: object
description: Account details associated with the transaction.
example:
lamports: 5000
owner: TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA
err:
type:
- object
- 'null'
description: >-
Error if the transaction failed, null if
successful.
example: null
innerInstructions:
type:
- array
- 'null'
description: >-
Inner instructions executed during the
transaction.
example: null
loadedAccountsDataSize:
type:
- integer
- 'null'
description: >-
Total size in bytes of all account data loaded
during simulation.
example: 413
logs:
type:
- array
- 'null'
items:
type: string
description: >-
Program execution logs from the transaction
simulation.
example:
- >-
Program
TokenzQdBNbLqP5VEhdkAS6EPFLC1PHnBqCXEpPxuEb
invoke [1]
- 'Program log: Instruction: Transfer'
- >-
Program
TokenzQdBNbLqP5VEhdkAS6EPFLC1PHnBqCXEpPxuEb
consumed 1714 of 200000 compute units
- >-
Program
TokenzQdBNbLqP5VEhdkAS6EPFLC1PHnBqCXEpPxuEb
success
replacementBlockhash:
type:
- object
- 'null'
description: >-
Replacement blockhash information when
replaceRecentBlockhash is enabled.
properties:
blockhash:
type: string
description: The replacement blockhash.
example: 6oFLsE7kmgJx9PjR4R63VRNtpAVJ648gCTr3nq5Hihit
lastValidBlockHeight:
type: integer
description: >-
The last valid block height for the
replacement blockhash.
example: 381186895
returnData:
type:
- object
- 'null'
properties:
programId:
type: string
example: 83astBRguLMdt2h5U1Tpdq5tjFoJ6noeGwaY3mDLVcri
data:
type: array
items:
type: string
example:
- Kg==
- base64
description: Data returned by the transaction if any.
example: null
unitsConsumed:
type:
- integer
- 'null'
description: >-
Total compute units consumed during the
simulation.
example: 1714
example:
jsonrpc: '2.0'
id: 1
result:
context:
apiVersion: 2.3.3
slot: 393226680
value:
accounts: null
err: null
innerInstructions: null
loadedAccountsDataSize: 413
logs:
- >-
Program TokenzQdBNbLqP5VEhdkAS6EPFLC1PHnBqCXEpPxuEb
invoke [1]
- 'Program log: Instruction: Transfer'
- >-
Program TokenzQdBNbLqP5VEhdkAS6EPFLC1PHnBqCXEpPxuEb
consumed 1714 of 200000 compute units
- >-
Program TokenzQdBNbLqP5VEhdkAS6EPFLC1PHnBqCXEpPxuEb
success
replacementBlockhash:
blockhash: 6oFLsE7kmgJx9PjR4R63VRNtpAVJ648gCTr3nq5Hihit
lastValidBlockHeight: 381186895
returnData: null
unitsConsumed: 1714
'400':
description: Bad Request - Invalid request parameters or malformed request.
content:
application/json:
schema:
$ref: '#/components/schemas/ErrorResponse'
example:
jsonrpc: '2.0'
error:
code: -32602
message: Invalid params
id: '1'
'401':
description: Unauthorized - Invalid or missing API key.
content:
application/json:
schema:
$ref: '#/components/schemas/ErrorResponse'
example:
jsonrpc: '2.0'
error:
code: -32001
message: Unauthorized
id: '1'
'429':
description: Too Many Requests - Rate limit exceeded.
content:
application/json:
schema:
$ref: '#/components/schemas/ErrorResponse'
example:
jsonrpc: '2.0'
error:
code: -32005
message: Too many requests
id: '1'
'500':
description: Internal Server Error - An error occurred on the server.
content:
application/json:
schema:
$ref: '#/components/schemas/ErrorResponse'
example:
jsonrpc: '2.0'
error:
code: -32603
message: Internal error
id: '1'
'503':
description: Service Unavailable - The service is temporarily unavailable.
content:
application/json:
schema:
$ref: '#/components/schemas/ErrorResponse'
example:
jsonrpc: '2.0'
error:
code: -32002
message: Service unavailable
id: '1'
'504':
description: Gateway Timeout - The request timed out.
content:
application/json:
schema:
$ref: '#/components/schemas/ErrorResponse'
example:
jsonrpc: '2.0'
error:
code: -32003
message: Gateway timeout
id: '1'
security:
- ApiKeyQuery: []
components:
schemas:
ErrorResponse:
type: object
properties:
jsonrpc:
type: string
description: The JSON-RPC protocol version.
enum:
- '2.0'
example: '2.0'
error:
type: object
properties:
code:
type: integer
description: The error code.
example: -32602
message:
type: string
description: The error message.
data:
type: object
description: Additional data about the error.
id:
type: string
description: Identifier matching the request.
example: '1'
securitySchemes:
ApiKeyQuery:
type: apiKey
in: query
name: api-key
description: >-
Your Helius API key. You can get one for free in the
[dashboard](https://dashboard.helius.dev/api-keys).
````