# Create datasets

URL: https://docs.hanzo.ai/docs/openapi/eval/post-eval-datasets

> Writes a dataset — the named set of graded examples a run scores a model against — under the caller's org and answers 201 with it.

`POST /v1/eval/datasets`

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

|               |                                         |
| ------------- | --------------------------------------- |
| **Address**   | `https://api.hanzo.ai/v1/eval/datasets` |
| **Method**    | `POST`                                  |
| **Operation** | `post_eval_datasets`                    |
| **Auth**      | `Authorization: Bearer $HANZO_API_KEY`  |

Writes a dataset — the named set of graded examples a run scores
a model against — under the caller's org and answers 201 with it.

The NAME is the key, not an id: posting a name the org already has updates that
dataset's description and metadata and keeps its original creation time, so this
is create-or-edit and never a duplicate. Its items are untouched.

Requires a validated principal; 401 without one. The org comes from the
validated owner claim, never from a client X-Org-Id, so a dataset can only ever
be written under the caller's own tenant. A description over 64 KiB is 400.

## Request

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

| Field         | In   | Type   | Required | Description                                                                                                                          |
| ------------- | ---- | ------ | -------- | ------------------------------------------------------------------------------------------------------------------------------------ |
| `description` | body | string | —        | Description is free text about what this set measures; over 64 KiB is refused.                                                       |
| `metadata`    | body | object | —        | Metadata is a free-form object stored with the set and echoed back verbatim.                                                         |
| `metadata.*`  | body | any    | —        |                                                                                                                                      |
| `name`        | body | string | yes      | Name is the dataset's org-unique handle and the segment that will address it, so it must match ^\[A-Za-z0-9]\[A-Za-z0-9.\_-]{0,63}$. |

## Response

| Status    | Body             | Meaning |
| --------- | ---------------- | ------- |
| `201`     | eval.datasetView | created |
| `default` | problem-details  | refused |

`201` body — 7 fields.

| Field         | In   | Type            | Always | Description                                                                 |
| ------------- | ---- | --------------- | ------ | --------------------------------------------------------------------------- |
| `createdAt`   | body | string          | —      | CreatedAt is when the name was first written, kept across later edits.      |
| `description` | body | string          | —      | Description is free text the org wrote about what this set measures.        |
| `items`       | body | integer (int64) | —      | Items is how many examples the set holds.                                   |
| `metadata`    | body | object          | —      | Metadata is the free-form object stored with the set, echoed back verbatim. |
| `metadata.*`  | body | any             | —      |                                                                             |
| `name`        | body | string          | —      | Name is the dataset's org-unique handle and the segment that addresses it.  |
| `updatedAt`   | body | string          | —      | UpdatedAt is when the description or metadata last changed.                 |

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

## Examples

**CLI**

```bash
hanzo eval datasets create --name <name>
```

**SDK**

**.ts**

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

const api = new EvalApi(new Configuration({ accessToken: process.env.HANZO_API_KEY }));
const { data } = await api.postEvalDatasets({ name: "<name>" });
```

**.py**

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

client = ApiClient(Configuration(access_token=os.environ["HANZO_API_KEY"]))
result = EvalApi(client).post_eval_datasets(name="<name>")
```

**.go**

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

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

**.rs**

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

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

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

**.java**

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

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

var result = new EvalApi(client).postEvalDatasets();
```

**HTTP**

```bash
curl -X POST https://api.hanzo.ai/v1/eval/datasets \
  -H "Authorization: Bearer $HANZO_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
       "name": "<name>"
     }'
```

**MCP**

MCP reaches **eval** through the `eval` tool, which names its 16 operations with its own verbs — this one among them, under a name only MCP declares. `describe` explains any of them:

```bash
curl -X POST https://api.hanzo.ai/v1/mcp \
  -H "Content-Type: application/json" \
  -d '{
       "jsonrpc": "2.0",
       "id": 1,
       "method": "tools/call",
       "params": {
         "name": "describe",
         "arguments": {
           "op": "list_eval_datasets"
         }
       }
     }'
```

---

[Eval API](https://docs.hanzo.ai/docs/openapi/eval) · [All Hanzo APIs](https://docs.hanzo.ai/docs/openapi) · [Interactive reference](https://docs.hanzo.ai/docs/openapi/reference)