Understanding how information is exchanged between Klaviyo and apps

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You will learn

Learn about how information syncs between Klaviyo and your third-party apps via an application programming interface (API). Most data exchanged via a Klaviyo integration is one-way: data is pulled into your Klaviyo account so you can leverage a broad scope of your customer's data. 

How integrations sync information to and from Klaviyo

Klaviyo’s API is a set of interfaces where data is exchanged between Klaviyo and other applications connected to your Klaviyo account. To initially integrate Klaviyo with another application, you’ll need to use an API key. An API key is a unique identifier tied to your specific account.

Klaviyo generates two types of API keys, both of which can be found in your account:

  • Public
    Your public API key, sometimes referred to as your Site ID, is the unique identifier for your Klaviyo account. This key cannot be used by a third-party app to access private information within your Klaviyo account.
  • Private
    Private API keys are used to read data from Klaviyo and manipulate sensitive objects, such as lists. They ensure the process of updating subscriptions and other customer information is secure and private. Private API keys should be treated like your password: kept in a safe place and never exposed to the public. You can generate new private API keys for different applications to trace the source of data being added to your Klaviyo account.

For more specific information regarding types of Klaviyo API Keys, see our API reference documentation.

Types of APIs

This guide refers to Klaviyo's v1/v2 legacy APIs. We are in the process of updating these guides, please check back later! For more information about the differences between legacy and new APIs, check out the comparison chart and new API overview.

There are different types of APIs out there, each defined by a set of protocols. Klaviyo has two distinct API types you can use: REST APIs and the Track and Identify APIs.


RESTis an architectural style that provides guidelines for platform-agnostic communication between applications on the internet. The Klaviyo REST APIs primarily communicate using a JavaScript Object Notation (JSON) format, which provides a structured layout for the information contained in the API messages. The following areas of your Klaviyo account (also known as endpoints) can be accessed via the Klaviyo REST API, allowing you to specifically control your:

  • Metrics
  • Profiles
  • Lists and segments
  • Data privacy
  • Campaigns
  • Templates

The metrics API allows you to manipulate event data within Klaviyo, whereas the profile API allows you to manipulate profile data.

Track and Identify APIs

The Track and Identify APIs allow you to track and identify actions that someone has taken. Most data involved in a Klaviyo sync is one-way; data is often brought into Klaviyo via these two APIs. The Track API imports a tracking action, such as a placed order or started subscription, whereas the Identify API imports identifying data, such as a birthday or a gender property.

To track events or identify properties in a third-party app, a code snippet may need to be added to the platform to sync events/properties back into Klaviyo. In many of Klaviyo's built-in integrations, these code snippets are automatically added to the third-party site. When you integrate with Shopify or BigCommerce, for example, it automatically installs code snippets to allow the use of sign-up forms.

If the code snippet doesn’t automatically install, you can manually add it to the third-party platform yourself. For assistance with this, see our guide on enabling onsite tracking for your ecommerce store. Once you set up your integration, you can sync different types of data into your Klaviyo account.

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