# Segments

> A segment is a saved filter over a mailing list. It lets you target a subset of contacts that match specific conditions — for example, "all subscribers in the Netherlands" or "everyone who signed up after January".

## What it is

Segments turn a flat mailing list into a queryable audience. Where a campaign sent to a whole list reaches every confirmed contact, a campaign sent to a list + segment reaches only the contacts that match. Segments are reusable: define once, apply to many campaigns and automations.

## Key concepts

- **Rule**: a single condition — a field, a comparison, and a value (e.g. "country equals Netherlands").
- **Comparison**: how a field is matched against a value. The available comparisons depend on the field type:
  - Text fields: matches / does not match.
  - Number fields: less than, equal to, greater than.
  - Date fields: before, after.
  - Checkbox / radio fields: matches the selected option(s).
- **Condition group**: one or more rules combined with **AND** or **OR** to form the full filter.
- **Segment**: a named, saved set of conditions attached to a mailing list.

## Common workflows

### Creating a segment

1. Open **Segments** in the navigation.
2. Choose **New segment**.
3. Pick the mailing list the segment applies to.
4. Add one or more rules using the available custom fields.
5. Combine them with `AND` / `OR` as needed.
6. Save with a descriptive name (e.g. "NL subscribers, signed up < 30 days").

### Using a segment in a campaign

1. Start a new campaign.
2. Choose the mailing list.
3. In the audience step, apply the segment.
4. The audience count updates to show how many contacts match.

### Editing a segment

1. Open **Segments**.
2. Open the segment, change rules, save.
3. Future sends using this segment use the new definition; past sends are unchanged.

## Limits and edge cases

- Segments are scoped to a single mailing list. To replicate a segment across lists, duplicate it.
- A segment's match count is evaluated at send time, so the audience may differ slightly from what you saw when designing the campaign.
- If a custom field referenced by a segment is deleted, the segment will need to be edited before it can be reused.

## Web routes

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

- `/segments` — list of all segments.
- `/segments/new` — create a new segment.
- `/segments/:id/show` — view a segment definition.
- `/segments/:id/update` — edit a segment.
- `/segments/:id/subscribers` — view the contacts that match a segment.

## Related

- [Custom fields](/llms/custom-fields.txt) — segments filter on field values.
- [Mailing lists](/llms/mailing-lists.txt) — segments are scoped to a list.
- [Campaigns](/llms/campaigns.txt) — apply segments when choosing an audience.