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

# Single Simulations

> Simulate a single transaction over JSON-RPC or the Simulation API to preview execution, balance and asset changes, logs, and the call trace.

Tenderly supports single transaction simulations via [RPC](/simulations/single-simulations#simulate-via-rpc) and [API](/simulations/single-simulations#simulate-via-api). Simulations are executed on the latest state of the chosen network.

Dapps and wallets can use single simulations to give their users a way to dry-run transactions before committing real assets. This gives them a preview of the transaction execution along with the detailed balance and asset changes that have occurred. Transaction previews
can help users build trust in dapps, approve only successful transactions, and prevent costly failures.

## Simulate via RPC

[Node RPC](/node-rpc/overview) allows you to read blockchain data and send transactions. But you can also simulate transactions on the Node. The advantage of simulating via RPC is that you can perform all these operations through a single RPC URL.

<Note>
  Simulations via RPC or API are only available on supported networks. Check out the list of [supported networks](/platform/supported-networks).
</Note>

Retrieve your RPC URL and the access key from the [Dashboard](https://dashboard.tenderly.co/register?redirectTo=gateways).

Go to **Node** > **Copy HTTPS URL** of the desired network.

```bash title="example" showLineNumbers theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
https://mainnet.gateway.tenderly.co/$TENDERLY_NODE_ACCESS_KEY
```

To simulate a single transaction via RPC, call the `tenderly_simulateTransaction` method. [See RPC reference](/node-rpc/rpc-reference?network=ethereum-mainnet\&method=tenderly_simulateTransaction).

**Example**

<Tabs>
  <Tab title="request">
    ```bash title="request" showLineNumbers theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
    curl https://mainnet.gateway.tenderly.co/$TENDERLY_NODE_ACCESS_KEY \
      -X POST \
      -H "Content-Type: application/json" \
      -d \
      '{
        "id": 0,
        "jsonrpc": "2.0",
        "method": "tenderly_simulateTransaction",
        "params": [
          {
            "from": "0xe2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2",
            "to": "0x6b175474e89094c44da98b954eedeac495271d0f",
            "gas": "0x7a1200",
            "value": "0x0",
            "data": "0x095ea7b3000000000000000000000000f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1000000000000000000000000000000000000000000000000000000000000012b"
          },
          "0xfc497b"
        ]
      }'
    ```
  </Tab>

  <Tab title="response.json">
    ```json title="response.json" showLineNumbers theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
    {
      "id": 0,
      "jsonrpc": "2.0",
      "result": {
        "status": true,
        "gasUsed": "0xb412",
        "cumulativeGasUsed": "0xb412",
        "blockNumber": "0xfc497b",
        "type": "0x0",
        "logsBloom": "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000200000000000000000000000000028000000000000000002000000000000000000000010000000000000000004000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000010000000000000000000000000040000000000000000000000000000800000",
        "logs": [
          {
            "name": "Approval",
            "anonymous": false,
            "inputs": [
              {
                "value": "0xe2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2",
                "type": "address",
                "name": "src",
                "indexed": true
              },
              {
                "value": "0xf1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1",
                "type": "address",
                "name": "guy",
                "indexed": true
              },
              {
                "value": "299",
                "type": "uint256",
                "name": "wad",
                "indexed": false
              }
            ],
            "raw": {
              "address": "0x6b175474e89094c44da98b954eedeac495271d0f",
              "topics": [
                "0x8c5be1e5ebec7d5bd14f71427d1e84f3dd0314c0f7b2291e5b200ac8c7c3b925",
                "0x000000000000000000000000e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2",
                "0x000000000000000000000000f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1"
              ],
              "data": "0x000000000000000000000000000000000000000000000000000000000000012b"
            }
          }
        ],
        "trace": [
          {
            "type": "CALL",
            "from": "0xe2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2",
            "to": "0x6b175474e89094c44da98b954eedeac495271d0f",
            "gas": "0x79bdb0",
            "gasUsed": "0x5fc2",
            "value": "0x0",
            "input": "0x095ea7b3000000000000000000000000f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1000000000000000000000000000000000000000000000000000000000000012b",
            "decodedInput": [
              {
                "value": "0xf1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1",
                "type": "address",
                "name": "usr",
                "indexed": false
              },
              {
                "value": "299",
                "type": "uint256",
                "name": "wad",
                "indexed": false
              }
            ],
            "method": "approve",
            "output": "0x0000000000000000000000000000000000000000000000000000000000000001",
            "decodedOutput": [
              {
                "value": true,
                "type": "bool",
                "indexed": false
              }
            ],
            "subtraces": 0,
            "traceAddress": []
          }
        ],
        "exposureChanges": [
          {
            "assetInfo": {
              "standard": "ERC20",
              "type": "Fungible",
              "contractAddress": "0x6b175474e89094c44da98b954eedeac495271d0f",
              "symbol": "dai",
              "name": "Dai",
              "logo": "https://coin-images.coingecko.com/coins/images/9956/large/Badge_Dai.png?1696509996",
              "decimals": 18,
              "dollarValue": "1"
            },
            "type": "Approve",
            "owner": "0xe2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2",
            "spender": "0xf1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1",
            "rawAmount": "0x12b",
            "amount": "0.000000000000000299",
            "dollarValue": "0.000000000000000299"
          }
        ],
        "stateChanges": [
          {
            "address": "0x6b175474e89094c44da98b954eedeac495271d0f",
            "storage": [
              {
                "slot": "0x6f18ad69436c83a0d8b2c05ee70fa64e30403b1755cc38ee9cb6245926b14b17",
                "previousValue": "0x0000000000000000000000000000000000000000000000000000000000000000",
                "newValue": "0x000000000000000000000000000000000000000000000000000000000000012b"
              }
            ]
          },
          {
            "address": "0xe2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2",
            "nonce": {
              "previousValue": "0x0",
              "newValue": "0x1"
            }
          }
        ]
      }
    }
    ```
  </Tab>
</Tabs>

## Simulate via API

Use the [simulate API endpoint](/api-reference) to simulate a single transaction with different parameters.

<Note>
  To use Simulations on Virtual Environments, we recommend the [Simulate RPC](/node-rpc/rpc-reference?network=ethereum-mainnet\&method=tenderly_simulateTransaction) and [Bundle Simulate RPC](/node-rpc/rpc-reference?network=ethereum-mainnet\&method=tenderly_simulateBundle).
  Otherwise, you may use [Virtual Environments Simulation API](/api-reference).
</Note>

The URL must contain your **account slug** and the **project slug**. Follow this [quick guide](/platform/account/projects/slug) to find the slugs.

```bash title="Simulation API endpoint on public network" showLineNumbers wrap theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
https://api.tenderly.co/api/v1/account/${TENDERLY_ACCOUNT_SLUG}/project/${TENDERLY_PROJECT_SLUG}/simulate
```

```bash title="Simulation API endpoint on a Virtual Environment" showLineNumbers wordWrap=true theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
https://api.tenderly.co/api/v1/account/${TENDERLY_ACCOUNT_SLUG}/project/${TENDERLY_PROJECT_SLUG}/vnets/{vnetId}/transactions/simulate
```

You also need to receive the API access token, which is sent with the headers. Learn how to [generate the API access key here](/platform/account/projects/api-tokens).

### Request payload

Send a `POST` request to the API endpoint. For full details on the request payload, see the [See API reference](/api-reference).

The simulated payload is similar to the `eth_call` JSON RPC call.

The fields below are required:

* `network_id` (string): ID of the network where you want to run the simulation.
* `block_number` (number): “latest” or the block number to be used for the simulation.
* `to` (string): The recipient address of the transaction.
* `from` (string): Address initiating the transaction.
* `input` (string): Encoded contract method call data.
* `gas` (number): Amount of gas provided for the simulation.

<Note>
  You can specify any sender address in the `from` field. Since Tenderly simulates *unsigned* transactions, you don't need
  to own an account's private key to simulate transactions from a specific sender.
</Note>

You can also specify the `simulation_type`, which can be full, quick, or ABI. This field is not required since the default is set to `full`. Learn more about [Simulation Modes](/simulations/simulation-modes).

When making API requests, add the `X-Access-Key` header with the value being the access token.

**Example**

Make sure to store the access key securely in a `.env` file.

<Tabs>
  <Tab title="request.ts">
    ```ts title="request.ts" showLineNumbers theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}

    dotenv.config();

    const simulateTransaction = async () => {
      const { TENDERLY_ACCOUNT_SLUG, TENDERLY_PROJECT_SLUG, TENDERLY_ACCESS_KEY } = process.env;

      const simulation = await axios.post(
        `https://api.tenderly.co/api/v1/account/${TENDERLY_ACCOUNT_SLUG}/project/${TENDERLY_PROJECT_SLUG}/simulate`,
        {
          network_id: '1',
          block_number: 16533883,
          from: '0xe2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2',
          to: '0x6b175474e89094c44da98b954eedeac495271d0f',
          gas: 8000000,
          gas_price: 0,
          value: 0,
          input: '0x095ea7b3000000000000000000000000f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1000000000000000000000000000000000000000000000000000000000000012b',
          simulation_type: 'quick',
        },
        {
          headers: {
            'X-Access-Key': TENDERLY_ACCESS_KEY as string,
          },
        },
      );

      console.log(simulation.data);
    };

    simulateTransaction();
    ```
  </Tab>

  <Tab title="response.json">
    ```json title="response.json" showLineNumbers theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
    {
      "transaction": {
        "hash": "0x7c1a33fb449b8d4eb5ec042d94d1c7ce2a5acae05f02af58ce4fd8b5c6beaf0a",
        "block_hash": "",
        "block_number": 16533883,
        "from": "0xe2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2",
        "gas": 8000000,
        "gas_price": 0,
        "gas_fee_cap": 0,
        "gas_tip_cap": 0,
        "cumulative_gas_used": 0,
        "gas_used": 46098,
        "effective_gas_price": 0,
        "input": "0x095ea7b3000000000000000000000000f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1000000000000000000000000000000000000000000000000000000000000012b",
        "nonce": 0,
        "to": "0x6b175474e89094c44da98b954eedeac495271d0f",
        "index": 0,
        "value": "0x",
        "access_list": null,
        "status": true,
        "addresses": null,
        "contract_ids": null,
        "network_id": "1",
        "timestamp": "2023-02-01T12:11:23Z",
        "function_selector": "",
        "l1_block_number": 0,
        "l1_timestamp": 0,
        "deposit_tx": false,
        "system_tx": false,
        "sig": {
          "v": "0x0",
          "r": "0x0",
          "s": "0x0"
        },
        "transaction_info": {
          "contract_id": "eth:1:0x6b175474e89094c44da98b954eedeac495271d0f",
          "block_number": 16533883,
          "transaction_id": "0x7c1a33fb449b8d4eb5ec042d94d1c7ce2a5acae05f02af58ce4fd8b5c6beaf0a",
          "contract_address": "0x6b175474e89094c44da98b954eedeac495271d0f",
          "method": null,
          "parameters": null,
          "intrinsic_gas": 21584,
          "refund_gas": 0,
          "call_trace": {
            "hash": "0x7c1a33fb449b8d4eb5ec042d94d1c7ce2a5acae05f02af58ce4fd8b5c6beaf0a",
            "contract_name": "",
            "function_pc": 0,
            "function_op": "CALL",
            "absolute_position": 0,
            "caller_pc": 0,
            "caller_op": "CALL",
            "call_type": "CALL",
            "address": "0xe2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2",
            "from": "0xe2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2",
            "from_balance": "0",
            "to": "0x6b175474e89094c44da98b954eedeac495271d0f",
            "to_balance": "0",
            "value": "0",
            "block_timestamp": "0001-01-01T00:00:00Z",
            "gas": 7978416,
            "gas_used": 24514,
            "intrinsic_gas": 21584,
            "storage_address": "0xe2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2",
            "input": "0x095ea7b3000000000000000000000000f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1000000000000000000000000000000000000000000000000000000000000012b",
            "nonce_diff": [
              {
                "address": "0xe2E2E2e2e2e2E2E2E2E2e2E2e2E2E2e2e2e2E2e2",
                "original": "0",
                "dirty": "1"
              }
            ],
            "state_diff": [
              {
                "address": "0x6b175474e89094c44da98b954eedeac495271d0f",
                "soltype": null,
                "original": null,
                "dirty": null,
                "raw": [
                  {
                    "address": "0x6b175474e89094c44da98b954eedeac495271d0f",
                    "key": "0x6f18ad69436c83a0d8b2c05ee70fa64e30403b1755cc38ee9cb6245926b14b17",
                    "original": "0x0000000000000000000000000000000000000000000000000000000000000000",
                    "dirty": "0x000000000000000000000000000000000000000000000000000000000000012b"
                  }
                ]
              }
            ],
            "logs": [
              {
                "name": "",
                "anonymous": false,
                "inputs": null,
                "raw": {
                  "address": "0x6b175474e89094c44da98b954eedeac495271d0f",
                  "topics": [
                    "0x8c5be1e5ebec7d5bd14f71427d1e84f3dd0314c0f7b2291e5b200ac8c7c3b925",
                    "0x000000000000000000000000e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2",
                    "0x000000000000000000000000f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1"
                  ],
                  "data": "0x000000000000000000000000000000000000000000000000000000000000012b"
                },
                "trace_index": null
              }
            ],
            "output": "0x0000000000000000000000000000000000000000000000000000000000000001",
            "decoded_output": null,
            "network_id": "1",
            "calls": null
          },
          "stack_trace": null,
          "logs": [
            {
              "name": "",
              "anonymous": false,
              "inputs": null,
              "raw": {
                "address": "0x6b175474e89094c44da98b954eedeac495271d0f",
                "topics": [
                  "0x8c5be1e5ebec7d5bd14f71427d1e84f3dd0314c0f7b2291e5b200ac8c7c3b925",
                  "0x000000000000000000000000e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2",
                  "0x000000000000000000000000f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1"
                ],
                "data": "0x000000000000000000000000000000000000000000000000000000000000012b"
              },
              "trace_index": null
            }
          ],
          "balance_diff": null,
          "nonce_diff": [
            {
              "address": "0xe2E2E2e2e2e2E2E2E2E2e2E2e2E2E2e2e2e2E2e2",
              "original": "0",
              "dirty": "1"
            }
          ],
          "state_diff": [
            {
              "address": "0x6b175474e89094c44da98b954eedeac495271d0f",
              "soltype": null,
              "original": null,
              "dirty": null,
              "raw": [
                {
                  "address": "0x6b175474e89094c44da98b954eedeac495271d0f",
                  "key": "0x6f18ad69436c83a0d8b2c05ee70fa64e30403b1755cc38ee9cb6245926b14b17",
                  "original": "0x0000000000000000000000000000000000000000000000000000000000000000",
                  "dirty": "0x000000000000000000000000000000000000000000000000000000000000012b"
                }
              ]
            }
          ],
          "raw_state_diff": null,
          "console_logs": null,
          "asset_changes": null,
          "balance_changes": [],
          "created_at": "2023-02-01T12:11:23Z"
        },
        "method": "",
        "decoded_input": null,
        "call_trace": [
          {
            "call_type": "CALL",
            "from": "0xe2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2",
            "to": "0x6b175474e89094c44da98b954eedeac495271d0f",
            "gas": 7978416,
            "gas_used": 24514,
            "address": "0x6b175474e89094c44da98b954eedeac495271d0f",
            "input": "0x095ea7b3000000000000000000000000f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1000000000000000000000000000000000000000000000000000000000000012b",
            "output": "0x0000000000000000000000000000000000000000000000000000000000000001"
          }
        ]
      },
      "simulation": {
        "id": "cc4d422b-149c-4043-83ec-d2670c9ffe2c",
        "project_id": "dfdc391a-a15d-4590-9aef-8691259c7df4",
        "owner_id": "7d5e8b1f-8bf8-4eae-a70f-fb7d354b1cc2",
        "network_id": "1",
        "block_number": 16533883,
        "transaction_index": 0,
        "from": "0xe2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2",
        "to": "0x6b175474e89094c44da98b954eedeac495271d0f",
        "input": "0x095ea7b3000000000000000000000000f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1f1000000000000000000000000000000000000000000000000000000000000012b",
        "gas": 8000000,
        "gas_price": "0",
        "gas_used": 46098,
        "value": "0",
        "status": true,
        "access_list": null,
        "queue_origin": "",
        "block_header": {
          "number": "0xfc497b",
          "hash": "0x0000000000000000000000000000000000000000000000000000000000000000",
          "stateRoot": "0x3a3fd616aa768fc45b78d02fbd216e6a49a19153f92a091f5c4e9a2bbe494ef1",
          "parentHash": "0x57067724ea963c92291770db13ff945f9b7e11689d2494ba318cea6cdab1c2e2",
          "sha3Uncles": "0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347",
          "transactionsRoot": "0x912f0d5b52a308205d1c1a9b15409cbd455b414ac2d2bcb5b13ef01a5b4a41d8",
          "receiptsRoot": "0xfdc2b958b59f3ded07e132764112429f8e2827ed0e1d67954e05ee1be5e7e203",
          "logsBloom": "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",
          "timestamp": "0x63da56eb",
          "difficulty": "0x0",
          "gasLimit": "0x1c9c380",
          "gasUsed": "0xcb7693",
          "miner": "0xdafea492d9c6733ae3d56b7ed1adb60692c98bc5",
          "extraData": "0x496c6c756d696e61746520446d6f63726174697a6520447374726962757465",
          "mixHash": "0x43f7931adf192e8addc95bfae45f9db586434110ef7eac2d765e4a4b9ed6de4e",
          "nonce": "0x0000000000000000",
          "baseFeePerGas": "0x32c42d070",
          "size": "0x0",
          "totalDifficulty": "0x0",
          "uncles": null,
          "transactions": null
        },
        "deposit_tx": false,
        "system_tx": false,
        "nonce": 0,
        "addresses": null,
        "contract_ids": null,
        "shared": false,
        "created_at": "2024-01-08T17:30:06.992859393Z"
      },
      "contracts": [],
      "generated_access_list": []
    }
    ```
  </Tab>
</Tabs>

## Explore use cases

* [**Preview transaction outcomes**](/simulations/transaction-preview): Identify and fix issues that could cause transactions to fail.
* [**Asset and balance changes**](/simulations/asset-balance-changes): Get exact dollar values for all balance and asset changes that will happen.
* [**Gas estimation**](/simulations/gas-estimation): Accurately predict the gas costs before sending the transaction.
* [**State overrides**](/simulations/state-overrides): Modify blockchain conditions like timestamps and contract data to test different scenarios.

## Where to go next

<Card title="Bundled simulations" href="" />

<Card title="Simulate via SDK" href="" />