# Custom fields

> A custom field is an attribute attached to a contact beyond the email address — for example, first name, country, signup source, customer tier. Custom fields drive personalisation and segmentation.

## What it is

The email address is the only required attribute on every contact. Everything else is a custom field. Each mailing list defines its own set of fields, so a "Newsletter" list can collect first name and country while a "Customers" list collects company size and account type.

## Key concepts

- **Name**: the short identifier you reference in merge tags (e.g. `first_name`).
- **Label**: the human-friendly label shown on forms and on the contact view.
- **Type**: how the field behaves. Available types include:
  - **Single-line text** — short free text such as a name or city.
  - **Multi-line text** — longer text such as a comment or address block.
  - **Email** — text validated as an email address.
  - **Number** — numeric input with optional minimum and maximum.
  - **Date** — date picker.
  - **Dropdown** — pick one option from a list.
  - **Checkbox** — tick one or more options.
  - **Radio** — pick one option from a small set.
- **Placeholder**: a hint shown inside the input on forms before the visitor types.
- **Default value**: a value pre-filled when the field is empty.
- **Required**: must be filled in to submit a form.
- **Global vs list-scoped**: global fields are shared across all lists; list-scoped fields exist only on one list.
- **Validation**: format rules tied to the type — for example, valid email syntax or a numeric range.

## Common workflows

### Adding a custom field

1. Open the mailing list.
2. Open **Fields** (or **Custom fields**).
3. Choose **New field**.
4. Pick the type, set the name and label.
5. Mark required if needed; add options for dropdown/radio/checkbox.
6. Save. The field appears on the contact, in form builders, and as a merge tag.

### Using a field in an email

In the template editor, insert a merge tag for the field where the personalised value should appear. At send time, MailCamp replaces the tag with that contact's value (or a fallback if the field is empty).

### Using a field in a segment

When building a segment, choose the field, an operator, and a value. See [Segments](/llms/segments.txt) for which operators are available per type.

## Limits and edge cases

- Renaming a field changes the label, not the underlying identifier — so existing merge tags keep working.
- Deleting a field removes it from forms, segments, and the contact view; values are not recoverable.
- Number and date fields support richer comparisons than text fields, so pick the type with segmentation in mind.
- Checkbox fields with multiple selections are filtered against each chosen option in segments.

## Web routes

Paths use `:id` as the placeholder for a field's identifier.

- `/fields` — list of all custom fields.
- `/fields/new` — create a new field.
- `/fields/:id/update` — edit a field.
- `/fields/manage` — manage and reorder fields.

## Related

- [Contacts](/llms/contacts.txt) — where field values live.
- [Forms](/llms/forms.txt) — where field values are collected.
- [Segments](/llms/segments.txt) — where field values are filtered.
- [Templates](/llms/templates.txt) — where field values are inserted via merge tags.