> For the complete documentation index, see [llms.txt](https://docs.internetobject.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.internetobject.org/schema-definition-language/data-types/bool.md).

# Bool

The **`bool`** type validates a boolean value. In data it is written compactly as `T`/`F` or verbosely as `true`/`false`.

> For the boolean *value* syntax, see [Booleans](/structure-and-syntax/values/booleans.md).

## TypeDef

A `bool` MemberDef accepts only the options below. Any other key is invalid.

| Option     | Type   | Description                                                             |
| ---------- | ------ | ----------------------------------------------------------------------- |
| `type`     | string | The type name `bool`. First positional value.                           |
| `default`  | bool   | Value used when the member is omitted. Second positional value.         |
| `optional` | bool   | If `true`, the member may be omitted. Shorthand: `?` suffix on the key. |
| `null`     | bool   | If `true`, the member may be `null`. Shorthand: `*` suffix on the key.  |

## Examples

```ruby
active: bool
---
~ T        # ✓ true
~ false    # ✓
~ yes      # ✗ not-a-bool
```

Optional with a default:

```ruby
verified?: { bool, T }    # optional; defaults to true when omitted
---
~ {}        # ✓ verified resolves to T
~ F         # ✓ verified is F
```

Nullable:

```ruby
flag*: bool               # nullable (value may be N)
---
~ N         # ✓ null
~ T         # ✓
```

## Optional, nullable & defaults

| Input                               | Result                   |
| ----------------------------------- | ------------------------ |
| `T`/`true`/`F`/`false`              | the boolean              |
| any other token                     | `not-a-bool` error       |
| `N`, key nullable (`*`)             | `null`                   |
| `N`, not nullable                   | `null-not-allowed` error |
| omitted, `default` set              | the default              |
| omitted, optional (`?`), no default | absent                   |
| omitted, required                   | `value-required` error   |

> **Use the `*` suffix for nullability.** The keyed `null:` option is part of the TypeDef but is not currently honored — see *Implementation status*.

## Implementation status (beta)

* Keyed `optional:` works; keyed `null:` is not yet honored — use the `*` suffix.

## See Also

* [Booleans (value syntax)](/structure-and-syntax/values/booleans.md)
* [TypeDef](/schema-definition-language/advanced-schema-concepts/typedef.md) · [MemberDef](/schema-definition-language/advanced-schema-concepts/memberdef.md)


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