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

# Campaign Personalization

> Use contact variables to personalize campaign content for each recipient

## Overview

Campaign personalization lets you pull values from your contacts into campaign emails. You can use built-in fields like `{{firstName}}` and `{{email}}`, plus custom variables such as `{{company}}`, `{{plan}}`, or `{{registrationCode}}`.

## How it works

<Steps>
  <Step title="Register variables on the contact book">
    Add the custom variable names you want to use, such as `company` or `plan`,
    on the contact book.
  </Step>

  <Step title="Store values on each contact">
    Save the matching values on each contact through the dashboard, CSV import,
    or API.
  </Step>

  <Step title="Use variables in your campaign">
    Select that contact book in your campaign and insert variables into the
    subject or email content.
  </Step>

  <Step title="Send the campaign">
    useSend replaces each variable with that contact's value when the campaign
    is rendered.
  </Step>
</Steps>

## Available variables

These built-in variables are always available in campaigns:

* `{{email}}`
* `{{firstName}}`
* `{{lastName}}`

Custom variables come from the contact book's variable list.

<Warning>
  Custom variables must be added to the contact book before they can be used in
  a campaign. Variable names can only contain letters, numbers, and underscores.
</Warning>

## Set up personalization in the dashboard

### 1. Add variables to your contact book

1. Go to [Contacts](https://app.usesend.com/contacts)
2. Create a new contact book or open an existing one
3. Add your variables as a comma-separated list, for example:

```text theme={null}
company, plan, registrationCode
```

### 2. Add values to your contacts

For each contact, save values for the variables you registered.

For example, a contact might look like this:

```json theme={null}
{
  "email": "jane@example.com",
  "firstName": "Jane",
  "lastName": "Doe",
  "properties": {
    "company": "Acme",
    "plan": "Pro",
    "registrationCode": "WELCOME-2026"
  }
}
```

You can add these values:

* manually from the contact editor
* through CSV import using matching column names
* through the Contacts API using `properties`

### 3. Insert variables in your campaign

1. Open or create a campaign
2. Select the contact book that contains your variables
3. Insert variables into the subject or email body

Examples:

```text theme={null}
Subject: Welcome to {{company}}

Hi {{firstName}},

You're currently on the {{plan}} plan.
Your registration code is {{registrationCode}}.
```

If a contact book is selected, the campaign editor will suggest the available
variables automatically.

## Fallback values

If a variable might be empty, you can provide a fallback value:

```text theme={null}
Hi {{firstName,fallback=there}},
```

This renders `there` when `firstName` is empty.

## Using the API

### Create a contact book with variables

```bash theme={null}
curl -X POST https://app.usesend.com/api/v1/contactBooks \
  -H "Authorization: Bearer us_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Customers",
    "variables": ["company", "plan", "registrationCode"]
  }'
```

### Create a contact with variable values

```bash theme={null}
curl -X POST https://app.usesend.com/api/v1/contactBooks/{contactBookId}/contacts \
  -H "Authorization: Bearer us_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "email": "jane@example.com",
    "firstName": "Jane",
    "properties": {
      "company": "Acme",
      "plan": "Pro",
      "registrationCode": "WELCOME-2026"
    }
  }'
```

### Create a campaign that uses variables

```bash theme={null}
curl -X POST https://app.usesend.com/api/v1/campaigns \
  -H "Authorization: Bearer us_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Welcome campaign",
    "from": "Acme <hello@acme.com>",
    "subject": "Welcome to {{company}}",
    "contactBookId": "{contactBookId}",
    "html": "<p>Hi {{firstName,fallback=there}}, your plan is {{plan}}.</p>"
  }'
```

## Best practices

| Best practice                                | Why it helps                                                         |
| -------------------------------------------- | -------------------------------------------------------------------- |
| Register variables before importing contacts | Keeps CSV columns and API properties aligned with the contact book   |
| Keep variable names simple                   | Makes templates easier to read and maintain                          |
| Use fallbacks for optional data              | Prevents awkward empty spaces when a contact is missing a value      |
| Test with a small segment first              | Helps you verify rendered output before sending to a larger audience |