> ## 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.

# Prefill the Simulator with a draft link

> Build a base64url-encoded URL that opens the Tenderly Simulator with a pre-filled transaction form, for sharing simulations from CI or tooling.

A draft link opens the [Tenderly Simulator](/simulator-ui/overview) with a pre-filled form. Nothing runs until the recipient clicks **Simulate**, so the link is safe to share in test reports, pull requests, or alerts.

A draft prefills a **single simulation**, not a [bundle](/simulator-ui/simulation-bundles). It populates one transaction form (one `row`); it does not reconstruct a multi-step bundle.

## URL format

The link is the Simulator's new-simulation route with a `draft` query parameter:

`https://dashboard.tenderly.co/<org>/<project>/simulator/new?draft=<value>`

`<value>` is the draft JSON payload, UTF-8 encoded, then **base64url**: standard base64 with `+` replaced by `-`, `/` replaced by `_`, and `=` padding stripped.

<Tip>
  For a one-off share you do not need a script. Fill the form in the Simulator and click **Copy draft link** in the page header (shown while the bundle has a single simulation). The rest of this page is for generating links programmatically, from CI, test reports, or other tooling.
</Tip>

## Quick start

A minimal raw-calldata draft is all most CI scripts need. The `to` address goes in `contractAddress`, and the calldata goes in `rawFunctionInput`:

```json theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
{
  "v": 1,
  "network": { "id": "1" },
  "row": {
    "contractAddress": "0xdac17f958d2ee523a2206206994597c13d831ec7",
    "from": "0xab5801a7d398351b8be11c439e05c5b3259aec9b",
    "inputDataType": "raw",
    "rawFunctionInput": "0xa9059cbb…"
  }
}
```

Encode that payload and append it to the URL:

```python theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
import base64, json

payload = {
    "v": 1,
    "network": {"id": "1"},
    "row": {
        "contractAddress": "0xdac17f958d2ee523a2206206994597c13d831ec7",
        "from": "0xab5801a7d398351b8be11c439e05c5b3259aec9b",
        "inputDataType": "raw",
        "rawFunctionInput": "0xa9059cbb…",
    },
}

draft = base64.urlsafe_b64encode(json.dumps(payload).encode()).decode().rstrip("=")
url = f"https://dashboard.tenderly.co/<org>/<project>/simulator/new?draft={draft}"
```

```javascript theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
// Node.js
const payload = {
  v: 1,
  network: { id: "1" },
  row: {
    contractAddress: "0xdac17f958d2ee523a2206206994597c13d831ec7",
    from: "0xab5801a7d398351b8be11c439e05c5b3259aec9b",
    inputDataType: "raw",
    rawFunctionInput: "0xa9059cbb…",
  },
};

const draft = Buffer.from(JSON.stringify(payload)).toString("base64url");
const url = `https://dashboard.tenderly.co/<org>/<project>/simulator/new?draft=${draft}`;
```

```bash theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
# Shell, reading the payload from payload.json (GNU coreutils)
DRAFT=$(jq -c . payload.json | basenc --base64url -w0 | tr -d '=')
# macOS fallback:
DRAFT=$(jq -c . payload.json | base64 | tr '+/' '-_' | tr -d '=\n')
```

## Top-level payload

| Field     | Type                         | Required | Description                                                                                                                                                                                                                                                                                                                                                                         |
| --------- | ---------------------------- | -------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `v`       | number                       | yes      | Schema version. Must be `1`.                                                                                                                                                                                                                                                                                                                                                        |
| `network` | `{ "id": string }` or `null` | yes      | Chain id as a **string** (`"1"` is Mainnet, `"56"` is BNB Chain, and so on). Must be a network enabled on the recipient's project, otherwise they get a "network not available" error and an empty form. Always set it. `null` is accepted but skips the contract lookup and leaves the form mostly unusable. See [Supported Networks](/platform/supported-networks) for chain ids. |
| `row`     | object                       | yes      | The form fields. See [`row` fields](#row-fields) below.                                                                                                                                                                                                                                                                                                                             |

## `row` fields

Only `contractAddress` is required. Omit anything you do not need. Omitted fields keep the form's defaults, and unknown extra fields are ignored.

### Contract and function

| Field               | Type                   | Description                                                                                                                                                                                                                                                                                                                                                                               |
| ------------------- | ---------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `contractAddress`   | string                 | **Required.** The "to" address. The contract and its ABI are fetched on the recipient's side when the link opens.                                                                                                                                                                                                                                                                         |
| `inputDataType`     | `"decoded"` or `"raw"` | Selects the function-input mode. Use `"raw"` with `rawFunctionInput`, or `"decoded"` with `contractFunction` and `functionInputs`.                                                                                                                                                                                                                                                        |
| `rawFunctionInput`  | string                 | Hex calldata (`0x…`) for raw mode. No ABI needed, which makes it the most robust option for scripts.                                                                                                                                                                                                                                                                                      |
| `contractFunction`  | object or `null`       | Decoded-mode function reference: `{ "name": string, "selector"?: string, "signature"?: string }`. `name` is required inside the object. `selector` (4-byte hex, e.g. `"0xa9059cbb"`) is optional but preferred: it is matched first and is exact for overloaded functions. Without it, matching falls back to `name` and may pick the wrong overload. `signature` is informational only.  |
| `functionInputs`    | array or object        | Decoded-mode argument values. Preferred: a **positional array** in ABI order, for example `["0xabc…", "1000000", ["0xa…", "0xb…"]]`. Values are strings, numbers, or booleans. Array and tuple arguments may be passed natively as nested arrays or objects, with no pre-stringifying needed. The keyed form `{ "input_0": … }` is also accepted (it is what the UI's Copy button emits). |
| `contractAbiImport` | string                 | Pre-fills the in-app "Edit ABI" field. Function matching on open uses the **fetched** ABI only, so this field does not make decoded mode work for unverified contracts. Use raw calldata for those.                                                                                                                                                                                       |

### Transaction parameters

| Field      | Type             | Description                  |
| ---------- | ---------------- | ---------------------------- |
| `from`     | string           | Sender address.              |
| `gas`      | string or number | Gas limit, e.g. `"8000000"`. |
| `gasPrice` | string or number | Gas price in wei.            |
| `value`    | string or number | Native-token value in wei.   |

### Block selection

| Field             | Type                      | Description                                                                                          |
| ----------------- | ------------------------- | ---------------------------------------------------------------------------------------------------- |
| `block`           | string or number          | Block number to simulate at. Omit for the chain head.                                                |
| `blockIndex`      | string, number, or `null` | Transaction position inside the block. `null` or omitted means the start of the block.               |
| `endOfBlock`      | boolean                   | `true` runs the simulated transaction after every transaction in the block (overrides `blockIndex`). |
| `usePendingBlock` | boolean                   | `true` simulates on the pending block instead of a fixed number.                                     |

See [Simulation Parameters](/simulator-ui/parameters#pending-vs-historical-block) for how block selection and transaction index behave in the UI.

### L2 parameters

These fields apply to OP-stack and Boba networks only.

| Field             | Type    | Description                        |
| ----------------- | ------- | ---------------------------------- |
| `depositTx`       | boolean | Mark as an L2 deposit transaction. |
| `systemTx`        | boolean | Mark as an L2 system transaction.  |
| `mint`            | string  | Deposit mint amount.               |
| `l1BlockNumber`   | string  | Originating L1 block number.       |
| `l1Timestamp`     | string  | Originating L1 timestamp.          |
| `l1MessageSender` | string  | L1 message sender address.         |
| `l1Turing`        | string  | Boba Turing data.                  |

### Overrides

| Field                  | Type   | Description                                                                                                                                                                                                                                                                                                                                       |
| ---------------------- | ------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `blockHeaderOverrides` | object | `{ "number"?: …, "timestamp"?: … }`, each a string, number, or `null`. Overrides the simulated block header.                                                                                                                                                                                                                                      |
| `stateOverrides`       | array  | Per-contract [state overrides](/simulator-ui/state-overrides): `{ "id"?: string, "contractAddress": string, "balance": string, "storage"?: [{ "key": string, "value": string }], "code"?: string }`. `id` is optional and generated when absent. `balance` is in wei (`""` means no balance override). `storage` keys and values are 32-byte hex. |
| `accessList`           | array  | [EIP-2930](https://eips.ethereum.org/EIPS/eip-2930) access list: `{ "address": string, "storageKeys": string[] }`.                                                                                                                                                                                                                                |

Two override types are UI-only and cannot be set in a draft. Configure them in the app after opening the link: **fund-address ERC-20 overrides** and **custom Solidity sources** (the in-app "Edit source" feature).

## Validation

Draft hydration is all-or-nothing. A missing required field, a wrong `v`, or any wrong-typed field rejects the **whole** payload: the recipient sees "This draft link is invalid or corrupted" and an empty form. There is no partial hydration, so a broken script fails visibly instead of half-working.

## Limits and tips

* Keep the final URL under **2000 characters**. The app refuses to copy longer links, and browsers and proxies may truncate them. Decoded calls with many inputs land around \~1900.
* **Discovering payload shapes:** fill the form in the Simulator UI, click **Copy draft link**, and base64url-decode the `draft` value. The result is a known-good payload for your exact use case, and it is the best way to get the advanced shapes (`stateOverrides`, `accessList`) right.
* The contract ABI is fetched when the link opens. If it cannot be resolved (an unverified contract), decoded-mode drafts open with the address filled but no function selected. Raw mode is immune to this.

For the form fields a draft populates, see [Simulation Parameters](/simulator-ui/parameters). To keep a modified state as a persistent environment instead of a one-shot simulation, use [Virtual Environments](/virtual-environments/overview).