---
"@context": https://schema.org
"@type": TechArticle
"@id": https://www.twilio.com/docs/segment/connections/functions/transformation-functions#article
headline: Transformation Functions
description: Use Segment Transformation Functions to enrich, transform, validate, or filter data anywhere within a journey.
url: https://www.twilio.com/docs/segment/connections/functions/transformation-functions
inLanguage: en
dateModified: 2026-07-27T04:19:18.000Z
author:
  "@type": Organization
  name: Twilio Developer Education Team
publisher:
  "@type": Organization
  name: Twilio
---

# Transformation Functions

Use Transformation Functions to enrich, transform, validate, or filter data anywhere within a journey.

> \[!NOTE]
>
> The Transformation Function is in private beta, and Segment is actively working on this feature. Some functionality may change before it becomes generally available. For access, reach out to your CSM or contact Segment Support.

## Create a Transformation Function

You can create a Transformation Function from the Segment catalog.

To create a new Transformation Function, follow these steps:

1. Navigate to **Connections > Catalog > Functions**.
2. Click **New Function**.
3. Select **Transformation Function**.
4. Write and test your function code.
5. Optional: Configure function settings.
6. Click **Next: Configure & Create**.
7. Provide a name, optional description, and optional logo.
8. Click **Create Function**.

The new function appears in the Functions catalog where it can be managed and reused.

## Using Transformation Functions

A Transformation Function becomes active after an instance is attached to a journey step. To attach a function to a journey step, navigate to your journey in the Segment app, add or edit a "Run Function" step, and select your Transformation Function from the available functions list.

## Coding a Transformation Function

Transformation Functions expose a single handler:

```js
async function onTransform (event, settings) {
  // custom logic
  // Return Only new fields (do not return 'payload')
  return {
    // my_computed_field: value
  };
}
```

The handler receives the following parameters:

* **event**: The event payload containing the current journey context.
* **settings**: The function settings configured for the journey step.

Within the handler you can do the following:

* Modify event fields.
* Make HTTP requests.
* Perform asynchronous operations.
* Compute derived values.
* Filter events.
* Throw supported errors.

## Settings

Use settings to configure reusable parameters without modifying function code.

To configure settings, follow these steps:

1. Navigate to **Connections > Catalog > Functions > Transformation Functions**.
2. Open an existing Transformation Function or create a new one.
3. Open the **Settings** tab.
4. Click **Add Setting**.
5. Enter a **Label**, **Name**, **Type** and **Description** for your setting.
6. Save the setting.

Supported setting types include:

* **Static Value**: a fixed value that the journey passes for every execution. Supported data types include:
  * String
  * Boolean
  * Array
  * Object
* **From input data**: A dynamic value where you can define the relative path of the key whose value is passed from the event payload.

Settings are available to the function during execution and can be configured for each journey step.

## Testing

You can test Transformation Functions within the code editor.

To test a function, follow these steps:

1. Open the **Test** tab.
2. Provide a sample payload or paste your own event.
3. Click **Run**.
4. Review:
   * Output event
   * Execution result
   * Console logs
   * Error messages

Testing allows you to validate function behavior before deployment.

## Output schema

You can optionally define the output schema from the Transformation Functions Code Editor. The output schema is used in the journey setup workflow to populate the journey context from the Run Function step that can be used in subsequent journey steps.

You can manually enter the JSON payload of the returned event or copy directly from the Test Output using the **Generate from Test Output** option.

## Errors and error Handling

A function execution is successful if it completes without error. You can throw an error to create a failure on purpose. To make sure the function works as expected, use errors to validate event data before processing.

Throw one of the following predefined error types to indicate that the function ran successfully, but the data was not deliverable:

* `EventNotSupported`
* `InvalidEventPayload`
* `ValidationError`
* `RetryError`
* `DropEvent`

This is similar to Source, Destination, and Insert Functions.

The errors listed are all permanent errors, except `RetryError`. When a `RetryError` is thrown, Segment retries the function with exponential backoff before permanently failing.

## FAQs

### What products support Transformation Functions?

Transformation Functions are available in Journeys.

### Can I reuse a Transformation Function?

Yes. A single Transformation Function can be attached to multiple journeys and journey steps.

### Can I make HTTP requests?

Yes. Transformation Functions can call external APIs to enrich or validate data.

### Can I configure different settings for different workflows?

Yes. Each function instance can have its own settings while sharing the same function code.

### Can I test my function before deployment?

Yes. The code editor provides a built in testing environment where you can run sample payloads and inspect the output.

### What happens if my function throws an error?

The behavior depends on the error type. Permanent errors stop processing, while `RetryError` causes Segment to retry execution before marking the invocation as failed.

### Can I roll back a deployed function?

Yes. Transformation Functions maintains version history and supports rolling back to previous deployed versions.