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

# Custom fields

> Extend subscriber profiles with your own attributes.

**Custom fields** let you store your own attributes on subscribers, then use them in [segments](/en/guide/segments), [campaigns](/en/guide/campaigns) and [automations](/en/guide/automations).

## Create a custom field

In **Custom fields**, open the field builder, pick a **type**, and configure its properties:

| Property                          | Notes                                                                                       |
| --------------------------------- | ------------------------------------------------------------------------------------------- |
| Display name                      | The human-readable label.                                                                   |
| Field key                         | Used in placeholders as `{{custom.<key>}}`. Lowercase letters, digits and underscores only. |
| Description                       | Optional explanation.                                                                       |
| Default value                     | Optional value used when none is set.                                                       |
| Required when editing subscribers | Makes the field mandatory in the subscriber form.                                           |
| Options                           | For **Single choice** and **Multiple choice** fields.                                       |

You can also set validation: min/max length, a regex pattern, min/max value or step, depending on the type.

## Field types

| Type                | Use for                                               |
| ------------------- | ----------------------------------------------------- |
| Text / Long text    | Short or multi-line text.                             |
| Number / Decimal    | Whole or fractional numbers.                          |
| Date / Date & time  | Dates, with or without a time.                        |
| Yes/No              | Boolean values.                                       |
| Single choice       | Pick one option from a list.                          |
| Multiple choice     | Pick several options.                                 |
| URL / Email / Phone | Validated formats.                                    |
| Computed            | A value derived from other fields via a logic editor. |

## Using a field in content

Reference a field in email content and merge tags with its key:

```
Hi {{custom.first_name}}, your plan is {{custom.subscription_tier}}.
```

<Warning>
  Unknown or misspelled placeholders are flagged by the campaign [pre-send analysis](/en/guide/campaigns#pre-send-analysis) and can block a send. Double-check field keys.
</Warning>

## Scope and status

* **Scope**: fields are either **System** (built in) or **User-defined** (created by you).
* **Status**: **Active** or **Archived**. Archive a field to retire it without deleting data; you can unarchive or delete it later.