Our v3 API is now available! Learn more by visiting the v3 developer portal. Creating new v2 API keys is no longer supported.

Constant Contact API v2

The Constant Contact API v2 is built on HTTP, uses Representational State Transfer (REST) design principles and supports JavaScript Object Notation (JSON) data-interchange format. Our REST API is simple to use, direct and concise, lightweight and optimized. This architecture enables us to support a variety of platforms, including web, desktop, and mobile apps based on the iOS and Android operating systems. In addition, we provide wrapper libraries for developing apps in multiple languages.

The Constant Contact v2 API is built on HTTP, is RESTful and:

  • Uses predictable, resource-oriented URLs.
  • Uses built-in HTTP capabilities for passing parameters and authentication.
  • Responds with standard HTTP response codes to indicate errors.
  • Returns JSON.

Base URL

All API URLs start with the following base part:


Getting an API key

Follow these steps to create an account and register your app with Mashery, and get an API key. 

NOTE: For developers who have v1 API keys, you will need to create new v2 API keys to use the v2 APIs. If you have generated OAuth 2.0 tokens for your users using a v1 API key, those tokens will continue to work with the v2 API keys required for the current APIs.


The Constant Contact API uses the OAuth 2.0 protocol to authenticate an application in order to access a user's Constant Contact resources. For more info, go to the Authentication page. We have created endpoints to help migrate app users to OAuth 2.0 authentication from Basic and OAuth 1.0a

Data Formats, Supported Methods & more

We provide lots of useful information about using our API on the API Data Formats & more page, including date & time formats, encoding, paginated output, parameter types, read-only fields, supported methods, and more.

API Endpoints Overview

Learn about all the API endpoints and supported methods on the API Endpoints Overview page. Each listed endpoint and method links to a documentation page that gives the details about that endpoint and method including the following:

  • The complete endpoint, including all path and query parameters with definitions and tips on their use
  • HTTP response codes
  • Sample JSON payloads for you reference
  • JSON Structure - all properties with definitions for the endpoint elements
  • Sample JSON Response - example of what the API returns for a successful call
  • Access to our API Tester - clicking Test API brings you to our API Tester that utilizes Mashery's I/O Docs feature.

Endpoint Method Documentation

To view the documentation for each method an endpoint supports, click the method button in the Methods section of endpoint page:. The active endpoint is displayed in blue: 

I/O Docs API Tester

You can build JSON payloads, make calls, see JSON responses, and experience how the API works using our API Tester. Click Test API adjacent to the endpoint URI on the documentation pages. You will need to log in with your Mashery/Constant Contact credentials. 

Endpoint and API Tester button

See the API Keys page for more info on getting credentials.