# Create forward backward

URL: https://docs.hanzo.ai/docs/openapi/train/post-train-clients-by-id-forward-backward

> Accumulates the gradients of a batch on the client.

`POST /v1/train/clients/{id}/forward_backward`

> [Train →](https://docs.hanzo.ai/docs/openapi/train) · [All API references →](https://docs.hanzo.ai/docs/openapi) · [Get started →](https://docs.hanzo.ai/docs/guides)

|               |                                                               |
| ------------- | ------------------------------------------------------------- |
| **Address**   | `https://api.hanzo.ai/v1/train/clients/{id}/forward_backward` |
| **Method**    | `POST`                                                        |
| **Operation** | `post_train_clients_by_id_forward_backward`                   |
| **Auth**      | `Authorization: Bearer $HANZO_API_KEY`                        |

Accumulates the gradients of a batch on the client.

## Request

3 fields, body `application/json` (required).

| Field  | In   | Type   | Required | Description                                                            |
| ------ | ---- | ------ | -------- | ---------------------------------------------------------------------- |
| `id`   | path | string | yes      | ID names the client.                                                   |
| `data` | body | any\[] | —        | Data are the examples: {prompt, completion} text, or tokenized datums. |
| `id`   | body | string | —        | ID names the client.                                                   |

## Response

| Status    | Body            | Meaning |
| --------- | --------------- | ------- |
| `200`     |                 | ok      |
| `default` | problem-details | refused |

`200` body — 1 field.

| Field    | In   | Type | Always | Description |
| -------- | ---- | ---- | ------ | ----------- |
| `(body)` | body | any  | yes    |             |

Failure carries the platform error shape — see [Errors](https://docs.hanzo.ai/docs/errors).

## Examples

**CLI**

`hanzo` has no subcommand for this operation — the CLI serves only what cloud's live route table confirms. Use HTTP or an SDK.

**SDK**

**.ts**

```ts
import { Configuration, TrainApi } from 'hanzoai';

const api = new TrainApi(new Configuration({ accessToken: process.env.HANZO_API_KEY }));
const { data } = await api.postTrainClientsByIdForwardBackward({ id: 'id', data: ["<data>"], id: "<id>" });
```

**.py**

```python
from hanzoai.cloud import ApiClient, Configuration
from hanzoai.cloud.api import TrainApi

client = ApiClient(Configuration(access_token=os.environ["HANZO_API_KEY"]))
result = TrainApi(client).post_train_clients_by_id_forward_backward(id='id', data=["<data>"], id="<id>")
```

**.go**

```go
cfg := hanzoai.NewConfiguration()
cfg.AddDefaultHeader("Authorization", "Bearer "+os.Getenv("HANZO_API_KEY"))
client := hanzoai.NewAPIClient(cfg)

resp, _, err := client.TrainAPI.PostTrainClientsByIdForwardBackward(context.Background()).Execute()
if err != nil {
	return err
}
```

**.rs**

```rust
use hanzo_client::apis::{configuration::Configuration, train_api};

let mut cfg = Configuration::new();
cfg.bearer_access_token = std::env::var("HANZO_API_KEY").ok();

let result = train_api::post_train_clients_by_id_forward_backward(&cfg, Default::default()).await?;
```

**.java**

```java
import ai.hanzo.cloud.ApiClient;
import ai.hanzo.cloud.api.TrainApi;

ApiClient client = new ApiClient();
client.setBearerToken(System.getenv("HANZO_API_KEY"));

var result = new TrainApi(client).postTrainClientsByIdForwardBackward();
```

**HTTP**

```bash
curl -X POST https://api.hanzo.ai/v1/train/clients/<id>/forward_backward \
  -H "Authorization: Bearer $HANZO_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
       "data": [
         "<data>"
       ],
       "id": "<id>"
     }'
```

**MCP**

MCP declares no tool for **train** — `tools/list` on `https://api.hanzo.ai/v1/mcp` names the products it does reach. Use HTTP or an SDK.

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