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

# clock

> Contract, placement, related fields and source examples for this Nika YAML field.

[Language reference](/reference/language/overview) / `clock`

## Meaning and placement

### → run

system (wall time, default) · virtual (the injected virtual clock · time becomes a contract input · a timeout: budget reads against it)

| Property        | Declaration                        |
| --------------- | ---------------------------------- |
| Requirement     | Optional in this object            |
| Schema location | `/properties/run/properties/clock` |
| enum            | \["system", "virtual"]             |

**In the same object:** [entropy](/reference/language/words/entropy)

[Schema source (use the pointer above)](https://github.com/supernovae-st/nika-spec/blob/c5ebbb7b862b68bc6cf7235efba61173b844afc6/schemas/workflow.schema.json)

## In a source template

Excerpt from `templates/fanout.nika.yaml`, source lines 58–67. This is a fragment, not a runnable workflow.

```yaml illustration theme={"system"}
  # A `timeout:` is a deadline, and a deadline needs a clock. Declaring it says
  # out loud which one: `system` is the ambient wall clock (the honest default);
  # `virtual` drives a simulated clock for deterministic tests.
  clock: system

const:
  collection_source: "./items"      # SLOT: where the collection comes from
  # Known answers for the fan-in law — computed by hand, never by a model.
  # `prove` feeds them through the SAME jq `survivors` uses; a drift between
  # the two is a red assert, not a quietly wrong report.
```

### Templates containing this field

| Template                     | Source                                                                                                                             |
| ---------------------------- | ---------------------------------------------------------------------------------------------------------------------------------- |
| `templates/fanout.nika.yaml` | [Line 61](https://github.com/supernovae-st/nika-spec/blob/c5ebbb7b862b68bc6cf7235efba61173b844afc6/templates/fanout.nika.yaml#L61) |

These are literal key occurrences in the source files, not an execution or conformance claim. [How to instantiate a template](/guides/templates).

## Contract and implementation

This page projects the named specification revision. Check [released engine status](/reference/status) and [the validation workflow](/guides/agent-authoring) before running a file. An optional field is not evidence that every engine supports every value.

Canonical identity: `language:word:clock`. Spec revision: [`c5ebbb7b862b`](https://github.com/supernovae-st/nika-spec/tree/c5ebbb7b862b68bc6cf7235efba61173b844afc6).

[How documentation stays connected](/reference/knowledge-system).