> ## Documentation Index
> Fetch the complete documentation index at: https://docs.timbal.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Type Validators

> Validators for type checking, JSON, email, and null validation

Type validators check the type and format of values, ensuring data conforms to expected structures.

<Note>
  Type validators generally don't use transforms since they check data types rather than string content. See [Validators Overview](/evals/validators#transforms) for transform documentation.
</Note>

## not\_null!

Checks that a value exists and is not null/None.

```yaml theme={"dark"}
output:
  not_null!: true
```

| Parameter | Type    | Description                                         |
| --------- | ------- | --------------------------------------------------- |
| value     | boolean | `true` to require non-null, `false` to require null |

<Accordion title="Examples">
  ```yaml theme={"dark"}
  # Ensure output exists
  output:
    not_null!: true

  # Ensure tool output exists
  get_weather:
    output:
      not_null!: true

  # Ensure specific field exists
  search_results:
    output:
      items:
        not_null!: true
  ```
</Accordion>

<Tip>
  Use `not_null!: true` as a first validator to ensure the target exists before applying other validators.
</Tip>

## type!

Checks that a value is of a specific type.

```yaml theme={"dark"}
output:
  type!: "string"
```

| Parameter | Type   | Description |
| --------- | ------ | ----------- |
| value     | string | Type name   |

### Supported Types

| Type     | Matches                |
| -------- | ---------------------- |
| `string` | Strings                |
| `int`    | Integers               |
| `float`  | Floating-point numbers |
| `number` | Any numeric type       |
| `bool`   | Boolean values         |
| `array`  | Lists/arrays           |
| `object` | Dictionaries/objects   |
| `null`   | None/null values       |

<Accordion title="Examples">
  ```yaml theme={"dark"}
  # String output
  output:
    type!: "string"

  # Numeric result
  calculate:
    output:
      type!: "number"

  # Array of results
  search_products:
    output:
      type!: "array"

  # Object response
  get_user:
    output:
      type!: "object"

  # Boolean flag
  validate:
    output:
      type!: "bool"
  ```
</Accordion>

## not\_type!

Checks that a value is NOT of a specific type. This is the negated form of `type!`.

```yaml theme={"dark"}
output:
  not_type!: "null"
```

| Parameter | Type   | Description                   |
| --------- | ------ | ----------------------------- |
| value     | string | Type name that must NOT match |

<Accordion title="Examples">
  ```yaml theme={"dark"}
  # Ensure output is not null
  output:
    not_type!: "null"

  # Ensure result is not a string (expect structured data)
  process_data:
    output:
      not_type!: "string"

  # Ensure not returning an error object
  validate:
    output:
      not_type!: "object"
  ```
</Accordion>

## json!

Checks that a string value is valid JSON.

```yaml theme={"dark"}
output:
  json!: true
```

| Parameter | Type    | Description                  |
| --------- | ------- | ---------------------------- |
| value     | boolean | `true` to require valid JSON |

<Accordion title="Examples">
  ```yaml theme={"dark"}
  # Ensure output is valid JSON
  output:
    json!: true

  # Combine with content checks
  output:
    json!: true
    contains!: '"status"'
    contains!: '"success"'
  ```
</Accordion>

<Note>
  The `json!` validator only checks that the string is valid JSON. It does not validate the JSON structure. Use `contains!` or `pattern!` for content checks.
</Note>

## email!

Checks that a string value is a valid email format.

```yaml theme={"dark"}
extract_email:
  output:
    email!: true
```

| Parameter | Type    | Description                          |
| --------- | ------- | ------------------------------------ |
| value     | boolean | `true` to require valid email format |

<Accordion title="Examples">
  ```yaml theme={"dark"}
  # Validate extracted email
  extract_contact:
    output:
      email:
        email!: true
  ```
</Accordion>

## Common Patterns

### Structured Output Validation

```yaml theme={"dark"}
output:
  not_null!: true
  type!: "string"
  json!: true
  contains!: '"id"'
  contains!: '"status"'
```

### Type-Safe Numeric Results

```yaml theme={"dark"}
calculate:
  output:
    type!: "number"
    gte!: 0
    lte!: 100
```

### Span Output Type Checking

```yaml theme={"dark"}
get_datetime:
  output:
    type!: "string"
    pattern!: "^\\d{4}-\\d{2}-\\d{2}"

search_products:
  output:
    type!: "array"
    min_length!: 1
```

### Validating Nested Fields

```yaml theme={"dark"}
get_user:
  output:
    type!: "object"
    
# Or validate specific nested fields
get_user:
  output:
    profile:
      name:
        type!: "string"
        not_null!: true
      email:
        email!: true
```