# Secure & Easy Integration with the Listbuilding API

Setting up an API key in KlickTipp is quick and straightforward. API keys are essential for connecting third-party providers to your KlickTipp account. In this guide, we’ll show you exactly how to create one step-by-step so you can start integrating with ease.

The Listbuilding API is a simplified, purpose-built subset of the KlickTipp API.
It is designed for easy contact subscription scenarios and does not expose the full Management API feature set.

## Subscription of Contacts

Each Listbuilding API Key is permanently linked to exactly one tag.
This tag defines the entire behavior of the subscription.

All API actions always apply to the contact in relation to this tag:

- contacts are added or updated with this tag
- the tag can be removed
- or the contact can be unsubscribed entirely


| Action | Description |
|  --- | --- |
| [Signin](/listbuilding-api#operation/api.subscriber.signin) | Creates or updates a contact and associates the tag linked to the API key. |
| [Signout](/listbuilding-api#operation/api.subscriber.signout) | Removes the tag of a contact associated with the API key. |
| [Signoff](/listbuilding-api#operation/api.subscriber.signoff) | Unsubscribes a contact via the API key and prevents further communication. |


## Step-By-Step Instructions

### Creating an API Key in KlickTipp

1. Go to **List Building → New List Building**.
2. Select the **Entry via API Key** button.
3. Assign a name to your list building.
4. Choose an opt-in process.
5. *(Optional)* Add a manual tag under **Additional Tagging**.
6. Copy the generated API key to your clipboard.
7. Click **Save**.


From this point on, the API key fully defines:

- the opt-in process
- the assigned tag
- the subscription behavior


Now your API key is ready! Use it to integrate with your preferred third-party provider and start connecting seamlessly.

### Subscribe a Contact via API Key

Once the API key is created, you can immediately use it to send API requests to KlickTipp via the Signin function of the **Listbuilding API**.

[View full API reference](/listbuilding-api#operation/api.subscriber.signin)

**Example Request**


```bash
curl -X POST \
  https://api.klicktipp.com/subscriber/signin \
  -H 'Content-Type: application/json' \
  -d '{
    "apikey": "{{API_KEY}}",
    "email": "alex.example@klicktipp.example",
    "fields": {
      "fieldFirstName": "Alex",
      "fieldLastName": "Example"
    }
  }'
```

### Data Field Types and Input Formats

When submitting contact data via the Listbuilding API, all field values must match
the field types and field keys configured in the KlickTipp account.

The Listbuilding API does not expose field metadata or field definitions.
Incorrect formats will result in validation errors.

For a complete overview of supported field types, input formats, and common mistakes, see:
[Data Field Types and Input Formats](/guides/data-field-types)

### Error Handling

The Listbuilding API follows the same error model as the KlickTipp Management API,
but only returns errors related to subscription and contact update scenarios.

Business and validation errors are typically returned with HTTP status 406 and
include a numeric error code in the response body.

Detailed explanations of error structures, field validation errors, and all
subscription-related error codes are documented here:
[Error Handling and Validation](/guides/error-handling)

## When to use the Management API instead?

Use the Management API if you need:

- dynamic tag selection
- opt-in process selection
- contact search or updates without tagging
- advanced automation control


## Summary

The **Listbuilding API** is designed for simple and reliable contact subscription flows.

It provides a lightweight integration approach that requires no complex authentication, no metadata lookups, and no dynamic configuration. A single Listbuilding API Key fully defines the subscription behavior, including the opt-in process and the associated tag.

This makes the Listbuilding API ideal for forms, landing pages, and external tools that need a fast and secure way to add or update contacts in KlickTipp without implementing the full Management API.

Remember that API access requires a [**Premium plan or higher**](https://www.klicktipp.com/de/preise/). If you’re not on the appropriate plan, you’ll need to upgrade to unlock this feature.