# Estimate a transaction

`POST https://api.rarebl.com/open/tx/estimate`

Estimates the fee of a transaction without building digests. It takes the same body as tx/build.

**Rate class:** compute (2 requests per second, burst 10, per IP). **Available since:** Open API v2.

## Request

Send a JSON body (`Content-Type: application/json`). No API key is needed: `X-API-KEY` is reserved and ignored.

Example: `curl -X POST "https://api.rarebl.com/open/tx/estimate" -H "Content-Type: application/json" -d '{"chain":"dash","from":"[\"XnL1FvTKqe6aWfB8NrvgbUMuWCEA3dNxfF\"]","to":"[{\"address\":\"XiM9Afap6UEb5LDkcWrg2YyA28hifkZZKM\",\"amount\":\"0.01\"}]","priority":"standard"}'`

## Parameters

| Parameter | Type | Required | Description |
| --- | --- | --- | --- |
| `chain` | string | Yes | The chain to build for. One of: btc, ltc, bch, dash, eth, tron. |
| `from` | array \| string | No | UTXO chains: an array of addresses we may spend from (watched on BTC/LTC/BCH, any on DASH). ETH and TRON: the sender address (one address). Use `from` or `inputs` on UTXO chains. |
| `inputs` | array | No | UTXO chains: exact inputs `[{"txid","vout"}]`, verified unspent with `gettxout`. Any UTXO chain. At most 10 inputs on the hosted endpoints. |
| `to` | array \| string | Yes | UTXO chains: recipients `[{"address","amount"}]` (one entry only). ETH and TRON: the recipient address (one recipient). `amount: "max"` sends everything less the fee. |
| `amount` | string | No | ETH and TRON: the amount in whole units (or `"max"`), as the SDKs send it. UTXO chains put the amount inside each `to` entry. |
| `change` | string | No | UTXO change address. Default: the first `from` address. |
| `feeRate` | string | No | Fee rate in sat/vB (UTXO). Use `feeRate` or `priority`. |
| `priority` | string | No | Fee choice instead of `feeRate`. One of: slow, standard, fast. |
| `rbf` | boolean | No | Signal replace-by-fee (BTC and LTC). Default true. One of: true, false. |
| `opReturn` | string | No | Optional OP_RETURN payload as hex. At most 80 bytes; UTXO chains. |
| `token` | string | No | ERC-20 (ETH) or TRC-20 (TRON) contract address for a token transfer. |
| `gasLimit` | string | No | ETH: gas limit. |
| `maxFeePerGas` | string | No | ETH: max fee per gas, Gwei. |
| `maxPriorityFeePerGas` | string | No | ETH: max priority fee per gas, Gwei. |
| `feeLimit` | integer | No | TRON: fee limit in sun. |

## Responses

### API200 (HTTP 200): OK

A Dash estimate.

```json
{
  "status": 1,
  "code": "API200",
  "message": "success",
  "data": {
    "fee": "0.00000226",
    "feeSats": "226",
    "vsize": 226,
    "feeRate": "1"
  },
  "go": null,
  "meta": {
    "requestid": "0123456789abcdef",
    "notices": []
  }
}
```

| Field | Type | Description |
| --- | --- | --- |
| `data.fee` | string | The fee in whole native units. |
| `data.feeSats` | string \| null | The fee in the integer base unit. |
| `data.vsize / feeRate` | number / string | UTXO: virtual size and the fee rate in sat/vB. |
| `data.gasLimit` | string | ETH only. |
| `data.energy / bandwidth` | number | TRON only. |

### API200 (HTTP 200): OK (TRON)

A TRON TRC-20 transfer estimate (energy and bandwidth).

```json
{
  "status": 1,
  "code": "API200",
  "message": "success",
  "data": {
    "fee": "13.9",
    "feeSats": "13900000",
    "energy": 65000,
    "bandwidth": 345
  },
  "go": null,
  "meta": {
    "requestid": "0123456789abcdef",
    "notices": []
  }
}
```

### API400 (HTTP 400): Bad Request

A parameter is missing or malformed. `data.param` names it (here `chain`).

```json
{
  "status": 0,
  "code": "API400",
  "message": "Unknown or missing chain.",
  "data": {
    "param": "chain"
  },
  "go": null,
  "meta": {
    "requestid": "0123456789abcdef",
    "notices": []
  }
}
```

### API409 (HTTP 409): Conflict

BTC, LTC or BCH: a `from` address is not watched and active yet. Start a watch with [address/watch](https://docs.rarebl.com/api/address/watch).

```json
{
  "status": 0,
  "code": "API409",
  "message": "This address is not watched yet.",
  "data": {
    "reason": "not_watched"
  },
  "go": null,
  "meta": {
    "requestid": "0123456789abcdef",
    "notices": []
  }
}
```

### API422 (HTTP 422): Unprocessable Entity

The selected inputs cannot pay the outputs plus the fee.

```json
{
  "status": 0,
  "code": "API422",
  "message": "The inputs do not cover the amount and the fee.",
  "data": {
    "reason": "insufficient_funds"
  },
  "go": null,
  "meta": {
    "requestid": "0123456789abcdef",
    "notices": []
  }
}
```

### API422 (HTTP 422): Unprocessable Entity

An output (often the change) is too small to be relayed.

```json
{
  "status": 0,
  "code": "API422",
  "message": "An output is below the dust limit.",
  "data": {
    "reason": "dust_output"
  },
  "go": null,
  "meta": {
    "requestid": "0123456789abcdef",
    "notices": []
  }
}
```

### API429 (HTTP 429): Too Many Requests

Rate limited (compute class: 2 requests per second, burst 10, per IP). A `Retry-After` header says how long to wait, in seconds.

```json
{
  "status": 0,
  "code": "API429",
  "message": "Too many requests. Please retry shortly.",
  "data": null,
  "go": null,
  "meta": {
    "requestid": "0123456789abcdef",
    "notices": []
  }
}
```

### API502 (HTTP 502): Bad Gateway

The node is unavailable, still syncing or timed out. Retry later with a short back-off.

```json
{
  "status": 0,
  "code": "API502",
  "message": "The node is unavailable or timed out. Please try again.",
  "data": null,
  "go": null,
  "meta": {
    "requestid": "0123456789abcdef",
    "notices": []
  }
}
```

## Notes

- Same body as [Build a transaction](https://docs.rarebl.com/api/tx/build), without signing. Use it to show a fee before the user commits.
- For network-wide fee levels, use [Recommended fees](https://docs.rarebl.com/api/fees/recommended).