> ## Documentation Index
> Fetch the complete documentation index at: https://runpod-b18f5ded-public-endpoints.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Input validation

Runpod's validator utility ensures robust execution of serverless workers by validating input data against a defined schema.

To use it, import the following to your Python file:

```py theme={"system"}
from runpod.serverless.utils.rp_validator import validate
```

The `validate` function takes two arguments:

* the input data
* the schema to validate against

## Schema Definition

Define your schema as a nested dictionary with these possible rules for each input:

* `required` (default: `False`): Marks the type as required.
* `default` (default: `None`): Default value if input is not provided.
* `type` (required): Expected input type.
* `constraints` (optional): for example, a lambda function returning `true` or `false`.

## Example Usage

```python theme={"system"}
import runpod
from runpod.serverless.utils.rp_validator import validate

schema = {
    "text": {
        "type": str,
        "required": True,
    },
    "max_length": {
        "type": int,
        "required": False,
        "default": 100,
        "constraints": lambda x: x > 0,
    },
}


def handler(event):
    try:
        validated_input = validate(event["input"], schema)
        if "errors" in validated_input:
            return {"error": validated_input["errors"]}

        text = validated_input["validated_input"]["text"]
        max_length = validated_input["validated_input"]["max_length"]

        result = text[:max_length]
        return {"output": result}
    except Exception as e:
        return {"error": str(e)}


runpod.serverless.start({"handler": handler})
```

## Testing

Save as `your_handler.py` and test using:

<Tabs>
  <Tab title="Command">
    ```sh theme={"system"}
    python your_handler.py
    ```

    Or with inline input:

    ```sh theme={"system"}
    python your_handler.py --test_input '{"input": {"text": "Hello, world!", "max_length": 5}}'
    ```
  </Tab>

  <Tab title="JSON">
    Create `test_input.json`:

    ```json theme={"system"}
    {
      "input": {
        "text": "The quick brown fox jumps over the lazy dog",
        "max_length": 50
      }
    }
    ```
  </Tab>
</Tabs>

This approach allows early detection of input errors, preventing issues from unexpected or malformed inputs.