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

# Functions

> Create and test reusable transforms for use in pipelines.

Functions package reusable event transformations. Open **Functions** to create, test, and maintain
function definitions independently of a pipeline.

## Languages

| Language   | Availability                                                       | Best for                                                       |
| ---------- | ------------------------------------------------------------------ | -------------------------------------------------------------- |
| VRL        | Always available                                                   | Parsing, normalization, filtering, redaction, and enrichment.  |
| JavaScript | Requires a build with `js-runtime`                                 | Logic that is easier to express with JavaScript.               |
| LLM        | API-configurable; requires `llm_eval_enabled` and a model provider | Low-throughput classification or enrichment with model output. |

MoleSignal validates and compiles a function during save. Invalid source does not become the active
function.

The current Functions workbench exposes VRL and JavaScript. LLM functions are an advanced API
workflow: the function source is the system instruction, the event is the model input, and
`params_schema.output_field` selects the output field (default `_llm_eval`).

## Test before saving

The function workbench contains the source editor and a JSON sample runner. The current
`POST /api/v1/functions/run` execution path runs VRL samples. JavaScript receives save-time syntax
validation when the runtime is compiled in, but unsaved JavaScript sample execution is not available
through this endpoint. LLM functions run only as pipeline steps.

Example VRL:

```vrl theme={null}
.service = downcase!(string!(.service))
.severity = upcase(string(.level) ?? "INFO")
if exists(.customer_id) {
  .customer = lookup("customers", .customer_id)
}
```

## Use a function

Add the function as a transform node in a pipeline. The pipeline stores the ordered steps and
passes the event through each function.

Deleting or changing a function can affect every referencing pipeline. Review usage before a
breaking edit.

## Permissions

* `functions.read` lists and opens functions.
* `functions.create` and `functions.edit` manage definitions.
* `functions.run` executes the VRL sample runner.
* `functions.delete` removes a definition.

<CardGroup cols={2}>
  <Card title="Pipelines" icon="diagram-project" href="/en-US/pipelines">
    Build source → transform → sink workflows.
  </Card>

  <Card title="Extend tables" icon="table" href="/en-US/extend-tables">
    Maintain lookup data for enrichment.
  </Card>
</CardGroup>