API
An API, or Application Programming Interface, is a defined set of rules and protocols that allows two software applications to communicate with each other.
Think of it as a formal contract between systems: the API specifies what requests one system can make, what format those requests must take, and what responses it will receive. When your email platform syncs a contact’s behaviour into your CRM, or your website form data flows automatically into your marketing automation tool, an API is usually doing the connecting work behind the scenes.
APIs are what make the modern marketing technology stack possible. Without them, every integration between tools would require bespoke development work. With them, platforms can be connected, data can flow in real time, and marketing teams can build workflows that span multiple systems without writing code from scratch. REST APIs are the most common type in marketing tech, though SOAP APIs are still found in older enterprise systems.
For marketing operations teams, understanding APIs at a conceptual level matters even if you are not writing the code yourself. Knowing what data is available via an API, what can be read versus written, and what authentication is required helps you have more productive conversations with developers and make better decisions about which platforms to connect and how. The difference between a manual data export process and a live API integration can be the difference between stale data and real-time personalisation.
What is the difference between a REST API and a SOAP API?
REST (Representational State Transfer) and SOAP (Simple Object Access Protocol) are two different approaches to building APIs. REST APIs use standard HTTP methods, are flexible in data format (usually JSON), and are the dominant standard in modern marketing platforms. SOAP APIs are older, more rigid, use XML exclusively, and are more common in legacy enterprise software. If you are integrating modern SaaS tools, you will almost certainly be working with REST APIs.
Do marketers need to know how to use APIs?
Marketers do not need to be able to write API code, but understanding what APIs do and what data they expose is increasingly valuable. Knowing that your CRM has an API that can push contact updates to your email platform in real time, for example, informs decisions about automation workflows, segmentation, and personalisation that would otherwise require a technical intermediary for every question. Basic API literacy makes marketing operations teams more self-sufficient.
What is an API key?
An API key is a unique identifier used to authenticate requests made to an API. It tells the receiving system which application or user is making the request and whether they have permission to do so. API keys should be kept private, rotated regularly, and never shared publicly. Most marketing platforms generate API keys within their developer or integrations settings section.