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

# Functions

> Inline utility functions for Tracecat expressions: transform strings, dates, numbers, lists, and JSON inside workflow and agent definitions.

## Overview

Tracecat expressions can call built-in functions with the `FN.<name>(...)` syntax.
Function results support bracket indexing such as `FN.range(0, 3)[0]`.
Function results do not support JSONPath wildcards or filters such as `FN.range(0, 3)[*]`.

Use in-line functions for one-line data transforms in action inputs.
For more complex logic, use a Python script or a custom UDF instead.

## Examples

Build a prompt or short string:

<CodeGroup>
  ```yaml Expression theme={null}
  prompt: ${{ FN.format("Investigate alert {0} with severity {1}", TRIGGER.alert_id, TRIGGER.severity) }}
  ```

  ```json Result theme={null}
  {
    "prompt": "Investigate alert al-123 with severity high"
  }
  ```
</CodeGroup>

Time manipulation for alert search windows:

<CodeGroup>
  ```yaml Expression theme={null}
  start_time: ${{ FN.to_isoformat(FN.now() - FN.minutes(15)) }}
  end_time: ${{ FN.to_isoformat(FN.now()) }}
  ```

  ```json Result theme={null}
  {
    "start_time": "2026-03-18T12:45:00",
    "end_time": "2026-03-18T13:00:00"
  }
  ```
</CodeGroup>

## Related pages

* See the [Functions cheatsheet](/cheatsheets/functions) for the full function reference and more examples.
* See [Expressions](/automations/core-concepts/expressions) for expression syntax and contexts.