# Assert

> Fail with a message when the expression is false.

| Node | Assert |
|---|---|
| Menu | Other › Assert |
| **Names in each format** | |
| .oink comp (JSON) | `"type": "OC_N_assert"` |
| .nk script | `Assert` ([how .nk import works](/docs/nuke-users/nk-import)) |
| Python | `nuke.createNode("Assert")` |
| Assistant (MCP) | `create_node(type="Assert")` |
| Tab search | `assert` |

![Assert properties](/shots/nodes/assert@2x.webp)

## Inputs and outputs

| Port | Name | Type |
|---|---|---|
| input 0 | Image | image |
| output 0 | Image | image |

## Knobs

Panel tab **Assert**, in panel order.

| Knob | Label | Type | Default | Range / values | .nk knob | Description |
|---|---|---|---|---|---|---|
| `expression` | expression | float | `1` | 0 to 1 | `expression` |  |
| `message` | message | text |  |  | `message` |  |

### Other knobs (Python, .nk and the assistant; not on the panel)

| Knob | Label | Type | Default | Range / values | .nk knob | Description |
|---|---|---|---|---|---|---|
| `gl_color` | Viewer Controls Color | float ×3 | `0, 0, 0` | 0 to 1 |  |  |
| `postage_stamp_frame` | Static Frame | int | `1` | -2147483648 to 2147483647 |  |  |
| `lifetimeStart` | Lifetime Start | int | `0` | -2147483648 to 2147483647 |  |  |
| `lifetimeEnd` | Lifetime End | int | `100` | -2147483648 to 2147483647 |  |  |
| `useLifetime` | Use Lifetime | boolean | `false` |  |  |  |
| `cached` | Cached | boolean | `false` |  |  |  |
| `bookmark` | Bookmark | boolean | `false` |  |  |  |
| `dope_sheet` | Dope Sheet | boolean | `false` |  |  |  |
| `clone_group` | Clone Group | string |  |  |  |  |
| `link_source` | Link Source | string |  |  |  |  |
| `link_overrides` | Link Overrides | string |  |  |  |  |
| `split_views` | Split Views | string |  |  |  |  |


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Sources: opencomp_core/nodes/utility/analysis.py, opencomp_electron/src/components/properties/knobSchema.ts, opencomp_core/nk/mapping.py